Watch some videos on Lake of the woods. The resorts have houses with troughs the length of the house rather than individual holes.
2″x2″ wall construction
one wall higher than the other for a single slope roof
5/16″ osb for all sheathing
2×4 for floor or 2×6 if they are larger houses.
use 2×6 or 2×8 for runners/skids.
watch menards or contact places that do or deal with roof tin. many times they have scratch and send deals. also contact a pole builder, they may have odd colors left from jobs for a good price.