You need to be holding the pistol for this to work as well as be playing an unpatched game.

When on FIVE go to the doors/barricades and break glass in the left middle corner.

Build the barricade back. Put boards on the front so it looks like a ladder.

There should be 3 or 4 boards on the inside. Go to the edge of the boards and jump. While walking towards the door jump 3 times and you will be high on the wall and untouchable by zombies.

Then jump to closest table and get dual rapid fire pistols.

Then jump to next table and get a quick reload python and next table for dual quick reload pythons.