The Length and Width parameters are for the building (walls), the foundation does slightly extend outside the wall area. I am not sure if this answers your question. Area is also the building area, independent of how many floors you have. Example length 10m and width 5m will be a building area of 50 square meters. If you have 3 floors then you get 150 square meters of floor area but the building area is still 10x5m = 50 square meters.
