How to put together an iPhone 4?

My uncle gave me his that he took apart to replace the screen and he took the whole thing apart all the way and I took it to get the screen fixed but they don't think all the parts are their and they want like 50$ to see what's missing how can I try and put it back together to see what's missing?

Go to "iFixit.com" and select the replace iphone screen, it will give you step by step direcetions on how to take it apart and put it back together. You should be able to see what is missing by the directions. You will have to search for iphone 4 screen replacement and then follow the steps.