Pick your table, drop terrain on it and see what it costs. Drag pieces to move them, tap one to rotate or remove it, then add the whole table to your basket. Postage is £3 per order however many pieces you buy.
Only you see this. Move each part until the building looks right, then save. "Sit on top of" stacks a storey or roof on another part. Untick tiny pegs or spares. Sizes are in millimetres; X is left/right, Y is front/back.