I'm interested (in coming up with designs), but as a person who's actively involved in design, we need to know the basic things:
1. colour of t-shirt
2. max size of graphics on shirt
3. theme
4. max number of colours / preferred colours
5. do the designer(s) get a cut of the profits?
I'm coming from a professional slant. So don't flame me for suggesting that designers who do this want to get paid. Anything is negotiable.
but just in case soft needs variety, or if someone out there wants a t-shirt design, I just outlined what designers would ask with respect to the project.