Society formation charges

If the number of prospective members (flat owners in possession) exceeds the minimum number of members for forming a housing society under the Maharashtra Co-operative Societies Act (MCSA), and is 60% or more of the number of flats in the scheme, society can be registered. You can approach the RoCS 4 months or later from the date on which you have such numbers and get the society registered, even inspite of active non-cooperation by the builder/promoter. I don't remember offhand what the min number is though - I think either 8 or 10. 

Another four months after registering Society, you can also get title to the underlying land conveyed to said Society - again, inspite of the builder's non-cooperation by applying to RoCS; and after his/her approval you can get a deed of "deemed conveyance" registered with the RoDocs. 

Both of the above are specified in the Maharashtra Ownership Flats Act (MOFA), 1963 which, along with the rules made under it, is something everyone in Maharashtra should read from end to end before even thinking about buying a flat. All the remedies you can imagine are already available to you there. You can get copies of both the MOFA as well as the MCSA (bare acts) quite cheaply in any law book store and at dirt cheap rates at a govt press office.