Hidden costs in Gurgaon: What builders don't tell you

My landlord just hiked the rent again, yaar, I'm genuinely fed up of renting and finally taking the plunge to buy in Gurgaon. Been looking at a 2BHK in Sector 82A, specifically Lion Infra Developers. Project looks decent, but I'm worried about the total cost. Brochure mein toh sab theek lagta hai, par I've heard so much about hidden charges that pop up just before possession. Like, what are those actual 'surprise' costs people face? Is it just maintenance, or kuch aur bhi hota hai? Also, construction-linked payment plan versus a down payment scheme, which one is smarter for an investor like me? My main goal is capital appreciation, so I want to leverage my funds wisely. Don't want to get stuck with a bad payment structure ya phir unexpected expenses that eat into my ROI. Any experiences with Lion Infra in Sector 82A regarding these issues? Kya negotiation possible hai on these hidden costs?