Builder floor

We have a 250 sq yard house. There are 2 owners of house(my father and my uncle). Our plot value is 2cr so each of them will get 1cr. Each of us will have a capital gain of 80 lakh and against of which we will buy new house so that we don't have any tax liability. My question is if i convert my house into builder floor , builder will give us 2 floors(1 floor each). And 50Lakh cash total. So what if after 2 yrs when builder floors are completed , i will sell my builder floor for 1.4cr , i ld end up getting more money than what i have got by selling just plot. Is it possible? And if yes then what will be the registered value of my flat as it will be needed to calculate capital gain. Does the purchase of our flat will be the same as what we bought it 25 years back or it will be new . And what is the process of registering our floor in our name and is the price of flat mentioned in these documents? Suppose the purchase price mentioned in document is 1cr and we sold it for 1.5 cr, we will have tax liability on 50 lakh. So that 1cr will be mentioned anywhere in any registration document?