I'm a prolific builder and love building out towns, as well as elaborate ships. However, currently, there's no way to tell where you're at with regards to the structure limit. You just hit it and then boom your project can't be finished. I think the places that would be perfect to display this are:
In the player inventory panel, show a count of how many structures are in vicinity of where the player is standing, and what the limit is (e.g. 7540 / 8250)
In the ship inventory panel, show a count of what's on the ship already and what the ship's structure limit is (e.g. 512 / 614 for a galleon)
An optional HUD display that you can turn on/off showing area or ship structure counts and limits