A vacant (land) lot is a lot without any building built on it. What is a name of a lot with a building (of any kind) built on that?
Can I name it an occupied lot?
I think an occupied lot sounds really weird, because lots are invariably vacant (there are only 273 instances of OP’s version in the Google Books link there, compared to 1,820,000 for a vacant lot).
And per Tom Au’s comment to Jim’s answer, improved is more evocative of the Monopoly board game. It’s also worth noting that the vast majority of written references to improved land seem to be in relation to agricultural land, where the term is defined here as…
Improved land includes all land regularly tilled or mowed, land in pasture which has been cleared or tilled, land lying fallow, land in gardens, orchards, vineyards, and nurseries, and land occupied by farm buildings.
I’d advise OP to call his one a developed site (12,900 written instances there).
EDIT: It’s worth noting that not only has an improved lot never had any real currency in the UK…
…but it’s also being replaced by a developed site over recent decades in the US…
Source : Link , Question Author : Dariusz Walczak , Answer Author : FumbleFingers