My 2BHK upgrade journey: Delhi investment queries

Green Valley Builders ke Dilshad Garden project mein hidden costs ka kya scene hai? I'm currently in a 2BHK in Vasant Kunj, thinking of upgrading to a 3BHK, maybe around ₹1.5 Cr. Builders often quote one price, but then PLC, parking, maintenance, sab add ho jaata hai. Kitna buffer rakhna chahiye for all-in costs? Payment plans mein pre-launch vs open-market pricing ka kya fayda hota hai? Should I push for a construction-linked plan for better leverage as an investor? Koi experience share karo, please.