Maps for multiplayer FPS game.

Me and my team are working on a FPS project which will be a “Tactical” multiplayer shooter game. Please note the emphasis on tactical because it will be really tactical and will require a lot of team work and coordination to win a game. The biggest factor in such a game is the maps which should have cover, choke points, vantage points etc
The problem is none of us isn’t able to make a single decent map and need help.
Any advice on what we should do to solve this problem is appreciated.