Where got so much.
The cost is just like buying from subsale property. You are paying the same thing.

10% as downpayment (for 1st and 2nd property. 3rd property onwards, you will need 30% as bank allow to loan you up to 70% MOF only)
5% as legal fees, stamp duty (assume no 1st home buyer waiver) and valuation fees

For newly completed property, be sure that the 1st owner bank already disburse out all money (especially the final 2.5% payment) to the developer.
Developer is still alive and active to avoid any delay in the later process.

Then that's it. There should not be any additional cost involve.