That said all rental projects that I know of in Maine and New Hampshire are all rented before they even finish construction.
EDIT: I'd also like to make a point about current regulation and zoning. It's not unusual for a developer to pay around $500,000 or more in state fees, environmental review, and layer time to get a new apartment complex approved. This requires insider connections and specialized knowledge of the municipality if you want it completed in a reasonable time frame. Partially this is because national building codes are more complicated then ever but more often building anything at all requires a zoning exception or amendment.
If you pull of the zoning maps for your town or city you'll likely find it riddled with parcels that have been cut out or otherwise exempted from the rest of the zone. This process can be expensive and take years to complete.
If a complex had 500 units, thats a negligible cost
[1] https://www.hcd.ca.gov/policy-research/plans-reports/docs/pa...
A house is made up of individual pieces of wood, drywall, bricks that are "under 10% of the cost" individually by the single piece but when stacked up they absolutely help explain the (much greater) cost of the house. It's going to be difficult to point to a single smoking gun; with housing it's death by a thousand cuts (in California development fees are one of the bigger ones).
See, e.g., https://www.accessmagazine.org/wp-content/uploads/sites/7/20...