Floors Allocation as per Land Share in Percentage.

Hello, I am really looking for some kind advice on the matter, Would really appreciate it. We have a 400 sq yards vacant plot in south delhi, with 2 owners (both with equal 50% Share of undivided land). Out of two 2 equal owners of the plot currently, one owner wishes to sell his 50% share of land and shift to some other place and second owner wishes to retain and build the house. I have a party who is a builder himself, he wishes to buy his 50% share and now he becomes the new 50% owner of the undivided land and i being the other 50% owner. My question is that i am entering into a construction agreement with the new 50% owner in the plot as he being the builder himself. He wants to make the building and then sell his allocated floors and move out of this place. His share of floors are SECOND+THIRD+TERRACE and i have the BASEMENT+GROUND+FIRST floors for which the construction cost will be shared. As the builder(the new 50% owner) has the second and the third floors with terrace he wishes to allot 25% land share to each floor. Whereas, i have the basement, ground and first floor, MY QUESTION IS BELOW(NEED ADVICE)- 1) Can i allocate the floors as 22.5% ground floor, 22.5% first floor and 5% for the basement. OR 2) 25% ground floor, 25% first floor and 0% for the basement. OR 3) Third option on someone's advice is that if i can buy 5% more share from the other owner and become 55% land rights owner by paying for the share to the other owner then, i can allocate it as 22.5% ground floor, 22.5% for first floor and 10% basement. I am confused as to how much allocation of the basement is necessary for future. What do i need to know to divide and allocate the land rights, as buying 5% rights is a very expensive affaire in south delhi. But on someone's advice asking here is 10% allocation to the basement really necessary? Thanks a ton to all and really looking forward to the answers.