A canon build, with a sword it would looks like the mech on the title screen. (HP: 325)
The cannons performed better than I expected, but their long attack cycle is a concern. Don't pick Destroyer Rounds; Cannons are already prone to damage overkill, but it just makes it worse.
When choosing between Root Reinforced Item and HP +15, you can get HP +15 by scrapping a useless lv3 upgraded item, so I'd prefer to choose root.