The closest thing to building a laptop yourself is getting an ECS Desknote. They have upgradable RAM, Processors, and harddrives(user serviceable), as well as easisally changable LCDs and apparently CD-ROMs.
Other than those, most laptops have next to no upgrade path...
I'm...not quite sure what your asking. The Desknote has 3 compartments on the bottom. One for the HD, RAM, and Processor. I also hear you can get new LCD screens(like a 15") and possibly DVD/CD-RWs for it.
These actually use standard processors(SocketA or whatever pentium 4s are) stnadard desktop DDR2100 RAM, but 2.5" harddrives