I built a 6 x 7 total span at my place about 7 years ago, all up was around 30k, I got someone to do the slab and I did the rest. I had to get a fire engineers report because I was close to the boundary, as well as a survey to check the boundry. I also had to get an engineer to do a PS 4 because I built it myself (about $500 from memory) I have one of those wind powered ventilators so no condensation issues, but it still gets hot in summer. I also increased the wall height to 3m so I could have a gantry beam running across with a chain block for lifting engines etc. I also spent a lot getting power put in, I have 20 x 10 amp plugs, 1 x 15 amp, and 1 x 32 amp for my welders. (Still not enough!!) Inside is lined with 12mm ply so I can attach stuff to walls, and it is insulated with noise stop batts to keep the neighbours happy!
Have fun!