Land share of Basement

I have a 390 sq yards property which I am getting reconstructed via a collaboration agreement with the builder. The reconstructed property will have basement, stilt parking, ground, first, second and third floors. The builder will take ownership of ground floor plus basement, while I will retain ownership of first, second and third floors of the reconstructed property. The collaboration agreement proposed by the builder states that land ownership rights are as follows: Basement: 10% Ground Floor: 22.5% First Floor: 22.5% Second Floor: 22.5% Third Floor: 22.5% The ground plus basement is going to be constructed and sold as a single unit by the builder. Thus there are 4 units with the following land share value: Ground + Basement: 32.5% First Floor: 22.5% Second Floor: 22.5% Third Floor: 22.5% My view is that all four units should have equal land share of 25%. My question is as follows: 1. Legally, does basement ownership provide a % of land rights to the owner? 2. Is the proposed division of 10% land share to the basement stipulated by Law OR is this flexible and up to the owner and builder to negotiate?