The hidden costs builders don't tell you

Last month, I almost got stuck with a builder payment trap. I was looking at a 3BHK in Sector 150 from M3M. Initial quotes for construction-linked plans seemed fine, but then hidden charges for PLC and OC came up, almost 10% extra. Mera budget hil gaya. Is this common with big builders like Godrej or ATS too? How do you guys manage these unexpected costs?