Builder alloted parking fully baised manner

Please state in which State is your building complex. Law in this matter changes from State to State and also with respect to under which Act of the State the association or society is registered. However the following can be said. Pending formation of an association and its registration, the builder has no right to allot parking lots. It is the prerogative of the registered association/society. It appears from your post that there are more parking lots than the number of flats. If so  one plot each can be alloted to each flat. If there is demand for a specific plot or specific plots from more than one member, the issue can be decided by taking lots. After all members have been allotted lots, the excess available can be allotted based on demand.