Maintenance of flat

Wanted to know whether it is right to pay maintenance of flat on superbuilt up area. My legal advisor has suggested that it should be on carpet area and not on builtup or super built up area. When spoke to the builder and society secretary they said since the expenses could not be met that is the reason they are charging maintenance on superbuilt up area. But according to my advisor he said if they have this difficulty then they need to increase rate /sq.ft and not the area. At present they are charging 2/sq.ft so to increase it by 3 or 4 sq.ft my flats carpet area is 565 sq.ft, built up is640sq.ft but the society charges me for 1000 sq.ft which they say is superbuiltup area. the builder even said that since you are the owners i can ask the secretary to charge your maintenance on carpet area but when you sell your property u will be priced on carpet area and not on built up or superbuilt up where u will hv to face a loss, kindly advice whether to pay maintenance on carpet area or built up area or super builtup.Will we face any problem while sale of this property after few years,