-roof are usually not accessible to public (suicide is often the reason why and many spots do have security nest etc). if a window can be opened, ok good. Above a certain height, it's lethal with certainty. Above 40 meters is often recommended to be sure, especially because no matter how you fall even legs first; but even before that chance of survival are very thin. It's one of the most fast and lethal method.
-your second question is the most important part actually. Easy? It seems so, just jump, 3-4 seconds later everything's done. But in fact it's not easy at all. As some other members stated it, SI is very hard to overcome with jumping. I guess that's why this is one rare method used statistically. Usually it's about few percent as a chosen method for both male and woman. there are exceptions, it's almost the half in honk kong but because it's all about skyscrapers there. There are also some countries where the statistics goes to 10% or a bit more, but generally it is a rare method. I did try, several times, to jump and it's not easy at all, believe me. The first attempt will tell you, because the more you try, the hardest so if you don't succeed to jump, you can give it up. So that's not easy, and ideally you should jump head first or at least in a way the head will land first (which is quite unpredictible and impossible to master).
-I won't advise you any methods. First because we can't do that. Secondly because it depends on people; what is true for someone (or easy) won't be for someone else.
What i can say is hanging (full suspension) is the most used method in almost any countries. It represents about half of the suicides for both men and women; sometimes even more.
SN is very popular here, i won't debate about that, i just think that poisonning is not as easy as many people here think it is. from a statistic point of view from the whole world, hanging full suspension is the most used method. If you inform yourself a bit, you'll realise it is quick, not so painful as you loose consciousness within seconds and no turning back if done properly..
But once again, it depends on you, what methods you can access in your own country, what do you mean finally by "easy", easy to set it up? easy as "painless"? easy to execute? easy to overcome SI?etc... Easy what??? All of this is damn subjective and differ from a person to another.