Before you go into a purchase decision, you need to note the stages of payment for a property that's still under construction. In the first 8 weeks, you should be looking at majority cash and CPF payment and the rest will be till the construction starts. Depending on which stage of the property progress when you make your purchase.
Majority of the initial payment include, booking fee, downpayment, stamp duty and additional buyer's stamp duty. It also depend on your citizenship and the number of property and loan you have. It is no easy calculation, which you should determine with a real estate consultant and a banker before entering a purchase decision.