most computer parts are made to be fit one speicfic outline e.g all hardrives will have similar screw hole placing and will be the same in size. laptop parts are very different. the laptosp ive opened pretty much all look different.
You can buy kits with all compatible parts. But you have to put every little thing in yourself. Ive seen them and their not atcualli all expensive. I know you can do that but I dont think you can go out, buy different parts and throw it all together like a desktop.