In games people who play heavy tanks often use reapers supported by welders often in a 1:1 ratio.
I wonder what it would be like to have a unit that acts as a moveable smaller range nano turret - we have builders/constructers but they dont auto repair units while moving etc.
It would be important to make any proposed unit less cost efficient than traditional builders. The advantage would be in the reduced intense micro often required to position and repair units (i.e. metal for metal a player that uses welders would be at an advantage).
Example for heavy vehicles
300m cost with two 'build rays' that can repair/assist 2 seperate units or the same one. Each ray having a build rate of 4m/s with a range 1/3 of a nano (Effectively like a welder with a slightly longer build range but lacking the ability to build or a weapon).
Settings to focus repairs on most badly damaged units in range up to a Priority set point which can change 30% 70% 100%. i.e. if set at 70% it would repair everything in range to 70% before repairing anything higher.
The above is a suggestion, maybe it should have stronger repair ability but cost more etc.