Private terrace maintenance charge

Q: Our building has 4 floors, the top floor has been converted as penthouse with private terrace and is owned by the builder. Our building owners have registered association formed. The penthouse is rented out by the builder. For the last 4 years the builder has been paying maintenance for the covered area only as per the rate fixed at Rs 1 per sqft.
At the last AGM meeting the point of charging the uncovered area was discussed out of the agenda published and it was agreed to charge atleast a minimum of 25% of total area of uncovered terrace area for penthouse. However, the builder refuses to pay the amount and says it cannot be charged.

What is the usual rule that is followed everywhere for private terrace/private uncovered area in an apartment premises