A builder contract differs from a resale offer in ways that matter: deposit schedules, construction delay clauses and what happens if the finished home does not match the floor plan are all builder-specific terms that a resale-focused buyer might not think to check.
Commission on a new-build purchase is negotiable, the same as on a resale, and in many cases the builder pays it directly rather than the buyer, so having your own representation on a purchase in the $400,000 range often costs the buyer nothing extra out of pocket.
Whether that applies to a specific builder and project is worth confirming before you sign anything. Get your hand-reviewed valuation from Joel Dyck.