First off, from the FAQ thread:
Q: Is it okay to ask people to make stuff for me, even if it’s for free?
A: Depends on what you're asking for. A lot of people in here will gladly do up a Website banner, a DVD cover, put your head on a Starfleet uniform, etc. while asking nothing in return except proper credit. On the other hand, you should probably think twice about asking people to do something they would normally earn hundreds or thousands (or tens of thousands!) of dollars for doing professionally. You should have no expectation of people doing that kind of work purely out of the goodness of their hearts, and don't be surprised if some of them take offense at even being asked to do so. They don't like the implication that their talents and efforts are essentially valueless. In short, you can ask, but at least try to understand what you're asking for.
That said, you've provided very little information. Is it absolutely necessary that you have a new class of ship? Would one of the dozens of existing designs work just as well for you? What era is this set? What size is the crew, and by extension, the ship? What function does the ship serve?
I don't think you'll have much luck in getting someone else to design your ship for you, but if you answer the above questions yourself, it can help you narrow down the design. Also, it sounds like you haven't written the story series yet. I'd start with that, then come back to the design. I would think you'd want to leave your options open for the stories, rather than get boxed in by a design from the start.