Im not sure if this has already been discovered. But I found a glitch
So Heres what you do
1. You can either have 2 or 3 people [ 2 For doing the glitch, 1 for proof]
2. Go to Cold seed
3. Go to the building nearest to Bravo Spawn point, the one attached to the 3 bins
4. Jump onto the yellow railing, then onto the overhang, then jump onto the pipes [ Eventually make your way to the roof]
5. Go to the center of the roof, And you should see an open window.
6. There is 2 air vents, jump into the right hand vent, [ Space between the vent and the wall ]
7. This may take quite a few trys to get caught so you can get up.
8. After you get caught, keep jumping, crouching and knifing, eventually you will get up onto the window, after that you can get up onto the roof
Im not sure if this is patched or not, i havent done it in a week or two, Let me know