3D-printing design suggestions

thejackalope thought this was worth mentioning said

I have an idea that I would like to get 3D printed, but I have pretty much ZERO graphic design experience. I have access to a 3D-printer through a co-worker, but I need help putting the actual design together.

Is there a design website that’s both super-noob friendly and free (or reasonably cheap) where I could work on getting this thing put together?