There are 2 ways of advertising an apartment for sale in Romania. The first is by the number of square metres of built space (known as 'suprafata construita') This takes in space occupied by walls, balconies, common areas etc. The second is by the number of square metres of useable space or 'suprafata utila'.
To be honest the built space measure is used more when selling houses rather than apartments. If you don't specify which measure you are using then it's going to be the first thing you are asked.