Congratulations and good luck with your "build"!
Mine isn't done yet, but we did a basic 8x8 kit (about $600) from a local hardware/home improvement store. You are in luck because they should be on sale now that summer stuff is going on clearance!! We dug out a 10x10 "pit" framed it in and filled it 6" deep with gravel. Pier blocks and 4x4 beams and then laid the floor that came with the kit. We added cement board to the floor and are putting in tile. I don't think we are going to insulate it, but will put a layer of pegboard on the inside. I promise to get pictures as it comes together!!
There is a whole thread in this section "OK, I admit it..."
Best wishes,
Michelle