Noida payment plans: Are we missing something?

Sector 145 mein Irish Infrastructure ka project dekh raha hoon. Kids moved out, ab chhota flat chahiye. Builder construction-linked payment plan push kar rahe hain, but down payment option bhi hai. Kya difference aata hai total cost mein? Aur yeh floor-rise premium, is it worth it? Samajh nahi aa raha.