New Chandigarh projects always hide costs

Budget finalised, loan pre-approved – ab New Chandigarh mein Manohar Singh and Company ka 3BHK dekh raha hoon. Currently in a 2BHK in Zirakpur, thinking of upgrading. Is it possible to negotiate well on the base price for a 3BHK around ₹1.2 Cr? Matlab, kitna percent tak? Aur all-in cost mein kya-kya hidden charges hote hain? Not just stamp duty, but like PLC, OC, ya maintenance advance. Builders sab upfront nahi batate na. Anyone have recent experience?