The building you choosed seems very high, so no matter how you fall you'll die instantly.
But i will be honnest with you, SI/fear of height/fear of the jump is damn hard to overcome normally so for someone who is also scared by height...
If you already experience high troubles and be shocked just by getting on the roof, it is clear that you will have lots of difficulties to execute it.
The only advise i could give you is to go straight, to not think, to not look down there. Just going straight at the edge of the roof and jump or let yourself go, no matter how. As i said at this height you'll die instantly you'll fell nothing even if you fall on your legs.
I don't think alcohol or drugs/meds will help.
This is from my own experience. It's not a universal truth as everyone is different, but it's already hard to jump for anyone, it's even harder if you're afraid by height. This method is more common in some big asian cities, but that's an exception. Those peoplelive there, they are used to see this height everyday, they just open their window and jump.
It would ask you years of practice including skydiving and therapy to overcome your fear.
As far as you have a spot placed very high, this method is seducing because it doesn't need material or setup,because it is quick, painless and close to 99,99% lethal above a certain height. It appears kinda romantic in some ways. But it is very very difficult to execute, i speak from my own experience.
The only way to make it, is to make it straight, and find the impulse, that's all. If you can't, there are some other methods you could consider.