Assigning unit specific actions to button grids

In nearly every RTS you have the option to select a unit and you see a menu based on the unity type (soliders, builders, herores, etc). Some of them (like in Company of Heroes) have a button that opens another sub menu eg; Button Defese Structures -> new menu with the defenses.

I have a conceptal question about these buttons. Assuming we use a 4x3 grid = 12 Buttons. Should I have prefabs for each button and load them, when ever a unit is selected to a specific position in the grid? Or...

Assigning unit specific actions to button grids