Scenario 1 (per square foot):
You agree a per square foot rate with the contractor. During the construction, the rupee undergoes massive devaluation. Plus there is inflation. Prices of construction materials goes through the roof.
Do you think the contractor will complete the house at the same per sq ft rate and take the loss himself? Of course not! Either he has already built in a big cushion/margin in the rate or more likely he will use cheaper materials to protect his margin.
Scenario 2 (cost plus):
You agree with the builder a percentage that he will get over the cost of project. So he charges you a percentage on every invoice and every payment for the project. He has to give you copies of all vouchers and receipts for every material he will purchase so you can do comparative price analysis. If he buys higher quality materials to increase his commission, then you also get higher quality house.
Which is the better option? What are the pros and cons of each?