It is 6ft 6" x 13ft 1". This size was chosen more to accommodate the size of my garden as its a fairly odd shape. It comfortably fits a couch and nail bar and one client at a time!! If you can fit a larger one in your space then do - mainly just for flexibility of where you put your equipment. If you are just doing nails then it is ample space. I intend to keep my couch pushed up against the end wall to create more space inside as I am more busy with nail treatments.
My husband who is very handy has built it all. The kit came flat packed from Dunster house in a zillion pieces. We laid a good base (£200) and I paid for upgraded floor and ceiling insulation and double windows on the cabin. He then painted it and added the electrics, fuse box,guttering, laminate floor etc. It has cost around £3k in total. I did buy the house in the winter sale though. I should imagine the price is creeping up now as we move towards summer and people start thinking about a summer houses for their garden projects!