The blessing (and curse) of DA mapping is that there really is no hard and fast rules about layout. In CS for instance you have bomb locations and player timing and sniper lanes and all that stuff. In DA you really just need stuff to dive from, flip off and slide under. That freedom means you can do whatever you want with your map but it also means you have almost no guidance. I totally understand how that can be paralyzing, so here's what I think you should do with this map.
This warehousy building could be the main play area for players and could provide great cover from campers and snipers. Extend it out, remove that hole (or work it into the design) and allow some player paths around and through it. Windows are always fun to dive through, and provide new ways for players to enter or exit an area.
Block off the rear area to enclose the space a little and force the player to move back into the battle area. Make an interior for the forge building to give an alternate route. I suggest keeping the wall between the alleyway behind the forge and the interior of the forge itself, ie no windows. I think that will keep both areas unique to each other and give the illusion of multiple areas in the map.
Extend this warehouse out and provide an interior for it. This could be a fun 'sidelane' and could give players more options to escape the inevitable rooftop campers. Bonus points if you use the concrete foundation to create some multi-level stuff inside the warehouse. I also drew in some random clutter and a roller door, which you could even set up to open and close like the one in da_megachat. Also block off the left side of the image, like in the previous image.
Clip that shit. Right now you can't walk or slide into there (you have to jump), and nothing's less cool than being stopped short as you're trying to boogaloo your way out of a tight spot.
I was just doodling some ideas for player paths here. This building would benefit from an interior.
Mostly you just need to block off the skybox a little and provide a few interiors. Try to make holes in the brushwork for players to dive/slide through. I noticed that you can slide under the deck of the main warehouse building, but it's so long that you end up stopping and sliding around prone underneath it to get out. It's cool to have sliding spots but they are best used as small escapeways or entry points for firefight areas. The idea is that a skilled player can use a small opening to escape from an imminent ass whooping, or to make a guns-blazing sneaky entrance to a play area. Also don't be afraid to use clip brushes to guide the player into an opening.
One of the things that usually gets me is the meta of a map. The backstory, the universe. It's reason for existence. A backstory and setting goes a long way to informing the map in all aspects, from layout to details to texture selection and spawnpoints and everything in between. Do you have a setting for this map? Here's an example of a meta setting that could apply to this map:
TJ Shipping and Wholesale is an criminal enterprise loosely disguised as an international logistics firm. They traffick weapons and illegal money for covert interested parties through their international supply chain. A recent shipment has arrived at the industrial end of the docks and has been intercepted by a rival street gang who are vying for an easy smash and grab. A firefight breaks out...
Ok I'm done typing now