Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download BuildR Procedural Building Generator Free.
BuildR 2 – Procedural Generator v2.27
Create a massive, fully explorable city with the most powerful, customizable and capable building generator on the Asset Store.
Leveraging multi core procedural mesh generation to allow you to CREATE COMPLEX BUILDINGS & ENDLESS CITIES within the Unity editor + at runtime WITHOUT sacrificing frame rate.
Generate EXPLORABLE INTERIORS through the custom built editor. Walk through the building you create!
? Generate buildings at runtime OR in the editor.
? Create ENDLESS BUILDINGS with complex EXPLORABLE interiors.
? Use custom models to accentuate your buildings and give them character.
? Generate ANY SIZE from small village houses to complex urban towers.
? Multithreaded parallel design takes generation off the main thread and free up your framerate.
? Supports all Unity platforms from mobile through to AAA.
? Asset based – create buildings that can be transferred easily between projects.
? Join a project that has been RUNNING, UPDATED and MAINTAINED for
OVER 7 YEARS!