So the amount you can construct is limited by the # of 2x2 tiles you can build on, a # based on size. But if you ever build on a tile, that tile is marked as "built" even if you cancel the construction immediately.
For example:
Step 1) 1 tile free
Step 2, tile has items in the build queue:
But if you cancel the construction - even on the same turn - you can't get the tile back:
