The formula to calculate the carpentry skill needed to build a single story building is Number of tiles + the number of outer walls. Note however that if you plan on adding to an existing building, the walls of the existing building that are inside the newly planned area are added to the total skill required, thus you may have to destroy those walls if they put the building over your skill level.

Freth's Building Skill Calculator Copy this calculator to your own Google Docs.

Each floor above the first floor requires a certain skill level.

Stone buildings require at least 30 masonry. You'll need to make bricks anyway, which will skill you up to that point.

NOTE: WO's formula (posted here for info only, does not apply to WU) for a single floor building is (Number of tiles + the number of outer walls)-5