You should see the lawyer before you sign the contract, otherwise, how the lawyer can help you if there is terms unfavorable to you? But anyway, it's always not late to see a lawyer.
I think defferent Builder has different contract, if you buy resale property, then all the contract are based on the same standard contract, it is fair to both seller and buyer. But for new house, the contract always depends on the Builder, so you need to read it more carefully.
For new house, the list price allways included part of the GST(about 64%GST), because the vendor can get the other part (about 36%) back from gov. For most new house, if price is not too expensive, land transfer tax can rebate.(only for first time home buyer)
This year, buy a resale house is a bad idea. most resaled house s are much expensive than a new one.