Check his legal standing as a builder. In Canada, we can search the 'Court of Queens Bench' to see if a builder has a disproportionate number of liens/claims against him.

As well, before putting an offer on the lot, I'd recommend viewing other houses they've constructed. Are the new homeowners happy? How long have they been in the house? Any new home warranty claims against the builder? Do you like the level of trims/finishes? Does he come in over budget, or on-budget?

Do they force you to use specific manufacturers for your cabinets, flooring, etc, or can you choose from your preferred vendors?

Any covenants/restrictions/caveats that could limit what you want to build?

(Covenants may limit the size, shape or colors of your house, while caveats are existing agreements in place, such as for lighting, communication/power lines, etc). They may also have a 'must build in X years' clause.

And with any property, what ELSE is nearby? Go check the registered legal plans, again to learn of proposed subdivisions, easements, and other 'things' that might change your view of the lot.

If in the city, find out how much it'll cost for hydro/sewer/water connections, as those add to your budget. If outside the city, you'll need a well and septic.