Potlatch 2 is a very good online tool, but it doesn’t come close to the features provided by a offline editor like Java OpenStreetMap (JOSM). With JOSM, one can more efficiently map buildings and houses with the following tools and plugins.

The plugins you will need…

• building_tools >v28412, for quickly drawing rectangular buildings
• piclayer >v27883, for overlaying images with 3 control points to use as reference image for mapping
• terracer >v28412, for quickly assigning house numbers and creating linked side-by-side houses (especially for areas such as Chinatown where old shophouses uses house numbers)

The quick way to map buildings

• Control+B to access rectangular building drawings, draw with 2 clicks
• Control+J to join these rectangular polygons (shift-click/ctrl-click to select multiple) into a single shape (with multi-polygon holes)
• Shift+T to quickly subdivide your main polygon into multiple labeled houses (useful for traditional chinese shophouses)

Hopefully this can speed up mapping for you!