3 in entranceway to the center (middle-floor), 3 on slope to high-floor
Tips & Tricks
There's only one armor, timing it will help you a lot.
If you know how to trickjump, there're plenty of access to certain areas where you can get just one way to normally go.
Near the Minigun there're two ways to get into the Flak Cannon passage. One of them requires you to go via two wood tables. These wood tables make some noise, thus giving your opponent a clue about where you are. By wall-dodge jumping from the side of the ramp facing the Minigun, you avoid this part.
You can also get access to the aforementioned shield by wall-dodge jumping from the top of the Shock Rifle ramp near the Minigun, avoiding to go through Flak Cannon/Lightning Gun. You might lose the chance to get these weapons, but you can get a really quicker shortcut to the Shield than if you go through the normal way.
The Flak Cannon, Lightning Gun and BioRifle passages (especially the latter) tend to be good places to get frags from three-rocket shots or well placed Shock combos.
Since it's just a 1on1 match, you don't need additional advices other than those of the above. In all reality, this match shouldn't even be hard, even when you're playing it in head-to-head matches.