So here's a baseline context of what I am thinking:
If you want to, in the comments you could list some stats and mechanics for the medigun and discuss the topic.
- Heals Buildings, however cannot Ubercharge them (that would be too op)
- Some sort of reward within the stats for healing engineer buildings on the condition that your team actually has an active Engineer.
- Fair downside(s) that would make the Medigun balanced due to its increased aforementioned healing variety factor.
- A unique Ubercharge type that can be used on players.
If you want to, in the comments you could list some stats and mechanics for the medigun and discuss the topic.