We did a self build with a brick/block and beam foundation with shiplap sides, full double glazing and LOTS of insulation (under floor, in roof, all walls).
We have running water to the Salon but no toilet. The house is close with a loo near the front door and havent had a client need to use it yet. We do have more of a problem with toilets as we are not on main sewerage and have to use ye olde sess pit for toilets which is why we use the house loo.
The whole building is about 45 feet by 13 feet. We have yet to finish it completely with verandas, paving, etc, because of the weather this year. We did use a large caravan/mobile home previously, and this building is heaps bettter. It is still a work in progress outside and think it cost aprox £20k. That includes the materials to finish it.
Only problem we have is it can get very very hot but the flip side is we use very little heating when its cold.
Viva the log cabin!