With Nano-Shield, you increase the survivability of whatever marine you target. By extension, you increase the survivability of the whole group which that marine is moving with. That makes the ability rewarding to use even if the marine isn't paying attention to the commander's exact orders. Nano-Construct is a much less dependable ability because the targetted player may stop to shoot at a skulk or wander off, or protect other building players. It seems to be less intuitive for the marine. I suggest that Nano-Construct be modified to target buildings and make them be built faster when a marine +uses them. The commander gets exactly what they want built without having to micromanage their personnel, plus it's intuitive for everyone. You can't cast the ability unless there's an unbuilt structure around to use it on.