The contract is not part of the purchase. It is the purchase
Buying off plan means paying, in stages and over years, for something that does not yet exist. There is no building to inspect, no separate title to search, and frequently no way to verify by looking at anything at all whether what you are promised will arrive. What you have instead is a document.
That is the whole of the difference from buying a resale property, where the risks sit in what has already happened to the building and are largely discoverable. Off plan, the risks sit in the future, and the only instrument that reaches into the future is the contract of sale and the protections registered around it. A buyer who negotiates the price hard and signs the developer's standard contract without changing a line has negotiated the wrong thing.
What to send us
The draft contract of sale and any reservation agreement, before signature rather than after. The plans, the specification and the price schedule. The name of the developer and of the registered owner of the land, and a note of any payment already made.