I like the idea of improving the building selection menu but I would explore other options first before making it into a 2-row widget - no need to expand the inteface's footprint unless necessary.
For one, I think it might be a good idea to add some filters, like "military buildings", "production buildings", "population buildings", etc. They could go as tabs.
Also, I would like there to be an option to either use smaller building icons or maybe even just text list.
