Noida under-construction: What unexpected issues come up?

Under-construction projects in Noida always make me nervous, honestly. Kids have moved out, so we're selling our big place, looking for a smaller, manageable 2BHK. Thought about under-construction flats for better pricing ya modern amenities. But yaar, possession delays ka darr rehta hai. Builders ka track record pata nahi chalta. Maintenance costs baad mein badh jaate hain? Are there hidden charges ya quality issues I should watch out for? Especially around sectors near hospitals. Any red flags log experience karte hain?