I am currently creating map of floor area ratio of each parcel of land in an area. Floor area ratio is the total floor area of the buildings on a lot divided by the total area of the lot of land they're on. I've used building height to estimate the number of floors and then multiplied that number by the area of the building footprint. the problem I am running in to is that there is often more than one building one a given lot and I can't find a way to group them and add their total floor areas before dividing by the area of the lot.
I have tried using intersect, spatial join and merge tools all with no success. Is there a simple way to do this that I have missed.