building outside the farm?

[ArcadioMorales]

is there any mod that allows building outside the farm?

[lizardmang]

Assuming you mean buildings, I'm pretty sure there aren't any mods that do that. I have a feeling that it may not even be possible.

In case you meant items (furniture, chests, etc.), they can be placed outside of the farm in vanilla, but they'll be destroyed if an NPC walks through them. I believe there's at least one fairly up-to-date set of maps online that show NPC paths.