Alright, so here is my outline for the Flash movie with Captain Cold as the villain:
*THIS OUTLINE ONLY DISCUSSES CAPTAIN COLD'S ORIGIN*
*BETWEEN THESE SCENES, YOU WOULD SEE SCENES OF FLASH'S ORIGIN AS WELL*
-The movie starts with slightly younger Leonard Snart being verbally abused by his father, followed by him storming out of his house and walking to his grandfather's house. We now see that they live an area covered in snow.
-When he arrives, he tells his grandfather he is taking his truck for drive (which happens to be an ice truck which his grandfather is the driver of).
-Basically, he hits the road heading South and anywhere away from home.
-He is derailed by a sudden explosion/collision.
-When he awakes, he sees a large perimeter set up with strange looking agents in suits gathering around an unidentified object that is covered in debris. When they notice Leonard awaking, they run and stop him from getting away. Two agents grab him and put him in a van. They demand him to tell them what he saw. He tells them he doesn't know. They bring him in for questioning at "The Agency".
-The person conducting the questioning is none other than Amanda Waller. She tells him she is with the government, and asks Leonard about what he saw, and he claims he isn't sure.
-Waller informs Leonard that they cannot simply let him go at this point, and that they will put him into solitary confinement if they have to. He becomes furious at what has transpired and demands justice. Waller gives him an offer... She asks him to become an agent for the Agency's newest project: Task Force X.
-Leonard reluctantly accepts.
-After being taken on a tour of the Agency facilities (including several different weapons technology experimentation labs), Leonard is put through training and such, forced to do the bidding of Waller and her Agency. Showing exemplary skills and leadership attitude, Amanda declares him Captain of Task Force X.
-His Task Force X uniform would look somewhat like this (except his gun would be a normal gun)
-Due to his quiet, uninviting demeanor, as well as his place of origin, his fellow agents coin him as Captain Leonard "Cold" Snart. One of his fellow agents even offers Leonard a "fist bump" during a trip to a mission, and when Leonard just stares at him, the other agent jokingly says "Jeez man, you really are Captain COLD aren't you..." Leonard despises his teammates, and despises the fact that they think he is emotionless by giving him a name like "Cold". But he keeps the frustration inside, just like everything else.
-Captain and his troop are sent on a mission to intervene in a weapons exchange between two terrorist groups in Keystone City. Upon arriving, he tells his troop to stay behind as he stealthily heads inside to check the place out. "Bold move, Cold" says one of his teammates as Leonard walks inside the building.
-After walking through a few corridors of nothing and nobody, Leonard finds himself standing before a room full of slaughtered women and children. He stands there perplexed, when all of the sudden, the Flash shows up behind the Captain.
-With nobody around, Leonard appears to have killed all of these people. Leonard denies it, yelling to his team to come and help him, but nobody shows. The Flash escorts Leonard to the police outside. Flash tells the police he heard reports of gunfire and screaming in the area, and when he arrived this is the only person he found alive. This is when he starts verbally damning his teammates for not helping him, and the cops and especially the Flash for falsely accusing him.
-Almost immediately after being jailed, he is told he is being transferred to another place for questioning. He is placed in a mobile holding cell, and when he arrives at the destination he finds himself back at Agency HQ.
-Waller approaches him and asks him what happened. He is at a loss, but he claims he did not murder those people... and he asks why his team did not back him up. She informs him that all his teammates completely vanished from their radar all at once just after Leonard entered the building.
-Amanda tells Leonard she doesn't understand how all of their highly trained men could have been taken out so quickly and easily. That's when Leonard comes to the conclusion that the Flash murdered all of the people, took and that he was being framed for Flash's action.
-He demands that Waller clear his name, but she tells him that this organization is a secret and that even if it weren't she could not have its name dragged through the dirt by the situation. This makes him snap. He realizes that, once again, he's become a victim of circumstance. Just like the truck accident, and just like his life back home.
-Waller informs Leonard that he is to have a surgery in the morning. One that will make him "think more clearly" and have communication at all times with the Agency.
-That night, Leonard sneaks into one of the Agency's labs to look into their database. He comes across the category "Speed". Under that, he looks into a folder dubbed "cyclotrons". He finds that the Agency has technology capable of slowing down particles, which he theorizes could help him take down the Flash. While he is in the lab, he notices a folder dubbed "Task Force X". He opens it to find another folder named "Codename: Suicide Squad". In which, he reads they plan on installing explosive chips into their agents brains as a way to prevent insubordination.
-This is when Leonard realized he had to escape. This organization, the police, his family, society, the Flash... they're all his enemy. It's time for him to go rogue.
-He quickly looks at the lab number written in the "cyclotron" file and immediately makes his way over to the technology's location within the facility. He arrives just as a scientist is leaving. He waits casually near the door until the scientist leaves. Leonard quickly stops the door from closing and enters the lab. He sees that there are two chambers, the one he is in (for observing) and the one through a window (where the experiments happen).
-He dawns a sleek looking parka and a visor somebody left inside the observing chamber before entering the freezing-cold, bright experimentation chamber.
-He approaches a strange-looking gun sitting on a platform inside the chamber.
-He picks it up, when all of the sudden, a security guard taps him on the shoulder. Out of shock, Leonard turns and accidentally pulls the trigger of the gun, making the guard freeze in his tracks with a screaming-look on the guard's face.
-This moment is the full realization of "Captain Cold". He is wearing the parka and visor, and he is holding the gun in his hands.
-Perplexed by what has occurred, Leonard stands in awe and observes the gun... but then realizes what just happened. He grabs some of the other equipment and plans from the lab and makes way for an exit. An alarm sounds.
-He runs into the Agency's experimental garage and seals the entrance behind him using ice from the the gun. He finds that all the garage hatches are locked, but he does find a large glass window on the wall, with a nifty-looking snowmobile perched right in front of it. He hops on, revs it up, and breaks through the glass.
-After escaping for a while across the snow, he realizes the snow terrain will run out shortly. He then looks down at the gun and realizes he can use it to create snow in front of him as he drives.
-He heads back to Keystone City to try to find, defeat, and get answers from the Flash. Along the way, he can possibly hold up a few banks and loot a couple of stores.
-A major part of the story would be Flash analyzing the murder scene. He can't seem to figure out how the gun that Leonard was holding could have killed all of the victims in that building.
Of course, more of the story would develop from here, but I just wanted to get the origin out of the way.
--- Oh, and by the way, in case you were wondering who it was that took out the members of Captain Cold's unit outside the building of the murder scene...
... that would be revealed in the sequel to be Reverse Flash's doing (through time travel). You see, since Zoom is so hell-bent on making Flash's life miserable, he tried to frame Flash for the murder of all those women and children. So, Zoom was the one that not only cleared the building of the terrorists, but also the one that filled it with murdered bodies. What Zoom didn't count on were Task Force X showing up at the scene before Flash arrived. So, he quickly disposed of them by carrying them all off far away and spinning them into dust. An oversight on his part was that Leonard was already inside, which left Barry to arrest Leonard rather than Barry look like the bad guy. So yes, Leonard was set up, but it wasn't set up for him. It was set up for Flash by the time-traveling Zoom.
This is a quick rough draft (I was just brain-storming really), so tell me if you find any errors.
Oh, and tell me how you would improve it. ;)