Here you are issued a building permit which expires over time... and if you don't complete your building in a specified period of time you are fined. You can extend the building permit period, but again you have to pay... this way there are "taxes" levied, no matter what, and the home owner is "encouraged" to finish to avoid punitive fines.

That is how it works around here... but no doubt in un-incorporated areas other dodges may apply.