Badshahpur under-construction projects are a gamble

Okay I'll be honest — I completely underestimated how confusing this process is. First time buyer here, looking at a 2BHK in Badshahpur. BLF Developers has an under-construction project that looks decent, but the delivery risk is making me nervous. How do you even evaluate that effectively? Also, beyond the flat price, I'm genuinely clueless about other costs. Like stamp duty, registration, interiors... my parents keep saying these add up huge. How much should I actually budget for these hidden costs? What's a realistic percentage to factor in?