Maintenance is equal for all flats irrespective of size of flats 

2) insurance charges depend upon area of flat .water charges depend upon number of inlets in flat 

3) property taxes depend upon area of flat 

4) if MC refuses to Listen to reason approach cooperative court for necessary reliefs 

- As per rule, the popular methods to calculate the maintenance fee for your apartment is ,Equal Fee for All, but it is common in the apartment, where all the flats are of same sized.

- The most commonly used method is Area Wise maintenance charge, A rate is fixed for one square feet and then multiplied by the total square feet area of your flat in this method. 

- The said method of calculation is not favorable for the members , and hence you can lodge a complaint before the managing committee against this rule , and if not agreed then you can approach the Registrar for the same. 

1. the costs of amenities and services which are shared in common by all the unit holders regardless of their unit area, have to be shared equally and not on basis of the unit area. The taxes like property tax is computed on basis of unit area and water charges are computed based on consumption or total number of water inlets provided in the flat. Except for the property tax and water charges, all other charges are to be borne equally by all the flat holders regardless of flat size. It is absurd that a flat holder owning a bigger flat is made to pay higher charges than that charged to the flat holder of a smaller flat, since both the flat holders would be using the common amenities and services equally. It is not that the bigger flat owner would use more security or more common electricity. So the reason given by your society that the charges are as mentioned in the bye-laws, does not seem to be a proper reason. Ask the society to produce the said bye-laws for your perusal. If there is indeed any such bye-law then that needs to be challenged legally as such a bye-law would certainly not stand the scrutiny of the law being unreasonable, onerous and arbitrary. 

2. there are no so called approved methods in Mumbai. Different societies follow different computations. Some are reasonable and some are completely absurd. 

3. if the MC does not relent you will have to take the matter legally. Begin by writing a complaint to the Dy. Registrar of Societies

4. your last query is irrelevant. That query is not for a lawyer to answer. You will have to engage a valuer for the same who can do comparative analysis of maintenance charges charged by different societies in the same vicinity and having almost the same amenities as your society

Housing Society cannot charge maintenance fee from members on the basis of property area (per square feet) of members. The Housing Society shall levy maintenance charges from the members as prescribed in Model Bye-laws No. 65-71. The ownership of the land is in the name of the housing society.

Water charges are charged on the basis of total number and size of inlets provided in each flat. 

Common electricity charges include all the electricity charges on account of compound lighting, borewell electricity expenses,, salary of lift operators,  passage lighting, lift electricity expenses etc., which should be divided  equally amongst all members respective of their flat  size. 

Maintenance charges are applicable according to the area of  the area of a flat under the Maharashtra Maharashtra Apartment Ownership Act, 1970 but not to one registered under the Cooperative Societies Act.

Generally two methods of charge maintenance to members of Housing Society and owners Apartment Association.
1) On the basis of are of property (square feet) (owners Apartment Association)

Under the Maharashtra Owners Apartment Act, 1970 one has to pay maintenance as per the percentage of ownership in proportion to the common areas and pay as per square feet. 

On the basis of provision of Model bye-Laws Number 65-71 of Co-operative Housing Society.

How Society’s maintenance has to be charged is explained in Part IX, Bye-laws 65 to 71 in the Bye-laws book of the year 2014.

Under the Maharashtra Owners Apartment Act, 1970 one has to pay maintenance as per the percentage of ownership in proportion to the common areas and pay as per square feet. 

The maintenance charge for a housing society is usually calculated based on a number of factors, including the size of the apartment or house, the amenities provided in the society, and the cost of maintenance of the common areas. Applicable provisions of law ( Maharashtra Cooperative Act, 1960 & Maharashtra Owners Apartment Act, 1970)

Dear client,

1. Proposed Maintenance Rates: The accuracy of the suggested maintenance rates is contingent upon the particular provisions delineated in the bylaws of the society. To comprehend the foundation for the computations, it is imperative that you carefully go over the bylaws. Should there be a significant disparity, you might choose to seek legal counsel.
2. Approved Calculation ways: There are a number of ways available for calculating maintenance charges, such as equal cost per unit or cost per square foot. The precise procedure may be decided upon by the members or specified in the society's bylaws. For information on acceptable practices, consult the Maharashtra Cooperative Societies Act, 1960 and the society's rules.
3. Relating to the Committee's Refusal to Modify: You might think about taking the following actions if the managing committee won't change the costing in spite of legitimate concerns: a)Ask the committee to explain their thinking in a conversation. b)Get the assistance of other residents who are also concerned if the problem continues. c)Under the Maharashtra Cooperative Societies Act, think about submitting a complaint to the Registrar of Cooperative Societies.
4. Estimated Maintenance Cost: Depending on the location, size, and amenities of the unit, the approximate maintenance cost may change. Comparing with other local societies that are comparable is a good idea. The Maharashtra Cooperative Societies Act is another resource you can consult for any rules pertaining to maintenance fees.

Hope this helps you.