What a lot is worth to build on. Look up the address and the county tells you the size, the zoning and the most you could put on it. Put in the house you would build and what it would sell for, and the page works down to the profit and back up to the most you could pay for the dirt.What a lot is worth to build on. Look up the address, put in the house you would build, and the page works down to the profit and back up to the most you could pay.