A filter or set of tabs by building type would be useful under the build menu. Right now I seem to rely on the mouse overs to find the buildings I can't recognize but being able to filter by production, housing, etc would be better. Not a huge issue though. I am sure after playing for a while they are easy to find quickly in the menu.
Another issue with the build menu is that it is not easy to determine why I can't build a building I just researched. One way this could be addressed is to include a city size number on the icon or in the rollover to indicate the city requirement.