Black Box is a Tier 5 map like Overwatch. Here's the map with the armories marked:
My strategy so far is to buy an ACR after wave 3, in preparation for the helicopter during wave 4. The first 3 rounds go for the bonuses, and then run around the map and take out the juggernaut and helo during round 4 like you do the first jugg on any map. Then hole up in the house being constructed in the top-left of the map, on the upper floor, right above the equipment armory.
The small red square is a sentry launcher pointing out the window, and I outlined the arc it swings. It's exposed to fire from the street which is why I chose an armored launcher. The goal is to thin out the enemies coming up the street, but there may be a better place for it somewhere else. The red square with a blue outline is me, looking toward the yellow arrows which are the directions the enemies come, up those two staircases and into the room at about the same point. So for regular waves it's great for funneling everyone into a small space where I can concentrate my fire, but still have an escape route.
The first time I played I just ran the map, exploring a bit, not really holing up anywhere, and got to round 14. The second time I played I did this strategy and got to round 24.
Juggernaut + Helicopter waves: 4, 9, 14, 19, 24, 28, 32, 36, 40...
The MilitantPo3t will have his strategy posted in the next few days, and I'll update this post with a link to his video as soon as it's up. UPDATE: Here it is. Go ahead a give it a "like" if it works for you.