Hidden property costs are a real shocker

Since last year I've been eyeing properties in Greater Noida, especially around Sector 30. I'm looking at a project by Grihapravesh Buildteck, under construction. My main worry is ki property price ke alawa kitna extra kharcha hota hai? Log bolte hain registry, stamp duty, fit-outs mein bahut paisa lagta hai. Is it true ki 20-25% extra budget rakhna padta hai? Aur under-construction project mein delivery risk kaise judge karte hain? Any red flags to watch out for in the agreement? Your experiences would really help.