Hello! I'm newer to BAR but I enjoy mocking things up. I saw some discussion about build menu clutter from there being a lot of duplicate units from naval / land.
I think this could be a UI improvement without using gridmenu by reducing the amount of duplicate units, which could leave room for titles or other organizational tabs on page itself (scrollable for longer build menus).
The game does have an auto-swap feature for land and naval buildings, but the cost between them can be very different, so they're currently separated. I think an on-cursor build suggestion displaying the cost would be a good compromise to free up build menu clutter and center the important building information where the user will be looking anyway (the cursor).