I bought a book a long time ago called "how to print t shirts for fun and profit" and there are plans for building a 4 color press in that. i think you can get it from
U.S. Screen Print & Inkjet Technology . the guy who wrote it is scott fresner, and hes got alot of good stuff on that site. from personal experience, the project might nickel and dime you to death. i built one myself a long time ago similar to his design. it worked, but not too well. the only bearings i could find to facilitate the rotary action of the screens would never be solid enough to hold tight registration.
this is just a suggestion, but before you start building a press, you may wanna look around and see if you can find a used one. i found a guy in my town who had an old harco 4 color press and he sold it to me for 100 dollars. it wasnt the best but it started me out, and it was better quality than what i built. but you may be better at building things than I. anyway, good luck!