Currently Engineers are very powerful with how much they can build with one person. Where are they getting all those materials?!?
I suggest a currency based system where Engineers start with 100 materials and can spend the materials on emplacements (placing an AT cannon would spend 50 materials for example).
These materials would be resupplyable through logistics trucks (standing near a Ural for example). These trucks could also resupply ammunition.
My opinion is that making fortifications is just a bit too easy/spammy at the moment.