On the contrary I think you should never be able to build on resources from the build menu since they're separate from the towns now. Instead, the resources that are within your area of influence and buildable should display a hammer icon on top of them to indicate that you can build them. If you don't have enough resources, display a greyed out hammer icon on top of them.
ya but in many cases, you have to do both for outside resources. Still a problem if i can use build menu on only SOME of the resources.
And having to search individually on your screen to build on resources just makes thing more tedious and adds more micromanagement to the player without adding the benefits of a more strategic gameplay.