JojoExtra tip. A soldier with gunboats can build fairly efficiently by standing next to a wall. Jumping, pressing crouch after he is in the air, and shooting a rocket above himself on the wall. If done correctly the soldier will take crater damage and can easily keep up the amount of damage needed to build without risking taking minicrits/needing the med to take the beam off of him so he can get low enough to escape plan build. This is also useful for arrow building if you want to use a soldier to do it.
useful but not optimal for soldier to do, you won't be arrow building at the maximum rate