It's a tough nut to crack, Gianluca. If you're correcting the perspective with software in post you need to be far enough away from the tall building to be able to get it all in your frame while leaving enough space around it to allow for straightening. But because most tall buildings are in cities and surrounded by other buildings getting a clear shot is nigh on impossible. It can be done though, if the circumstances are right. Your other alternatives are to accept the fact that it's a tall building and shoot up, or to frame and accentuate abstracts of the building. I have a couple of shift lenses that I use from time-to-time. One is a Canon 24mm Tilt-Shift and the other is an Olympus 35mm Shift (no tilt) lens. But most of the time I correct perspective in the post-processing phase. In the past I have relied on getting verticals right just by "eye-balling" the vertical adjustment in the Lightroom Transform module, and going with what looks best. But recently I've used the "Guided" feature, which works quite well I think.