Nice game, I really like the concept.
I've played it alone and it's still playable. Due to the 8 way direction sometimes its difficult to correctly aiming the ranged attack, maybe add some kind of aim assistance to target the nearest target to the player facing direction.
Also could be nice if the players could build different types of building.
Additionally, instead of ranged/melee, I would allow the players to select only 2 between a range of spell/skills (during the build), these skills/spells could be enhanced with gold.
Could be useful to allow the players to trade golds, or share the gold bank.
Keep it up man, it's a good starting point