There are a lot of people out there that like going to stores and picking out one of those model kits that they like and simply build it and stick it on their shelf but are there many people out there that have all kinds of parts and build them to their liking? This is what people call custom model building and it is quite popular.
Where Does This Occur?
Well by the looks of things it would seem that a lot of this kind of thing comes from the movie industry and when it comes to making a film you cannot simply use a pre built model kit. Movies would be pretty stupid if they used pre made model kits and this is because you would have a lot of movies featuring the same kinds of models!!
What a film company usually does is get someone to come in to create the best scale models that they can from parts found all across the board. Helicopters are created with RC helicopters and the same goes for things like RC aircraft. It is actually very difficult now to be able to tell what is the difference between CGI, real life and model kits whereas back in the day you could really tell they were all models.
Of course on top of this you will see a lot of people that just build up various things for a bit of fun. Some of the best examples that I have seen of people doing this are usually mixed with train sets because having a train set encourages people top be more creative.
Of course some people just collect the same kind of thing and get loads of them like the Lego video at the start of the post!