Power
How does world domination sound? Because that's exactly what you get when you become a Mason. After all, you're joining a fraternal order that dates back centuries and counts some of the most influential people in history among its members. Now you get to learn the secret rituals passed down through...
Apologies. Apparently we were thinking of Freemasons, not stonemasons. Now to remove this tinfoil hat...
Stonemason power is much different from your normal, everyday, take-over-the-world power. By and large, the most power a stonemason has involves cutting and shaping various kinds of stones. That's actually pretty cool when you think about it. You're smashing the building blocks of the earth, billions of years old, and carving them into shape to create fortresses and bridges (and fabulous decorative walkways).
Depending on how much of a craftsman you are, you might even be able to carve yourself a little niche following with statues or columns. The carver is a specifically artistic kind of stonemason, and is responsible for many of the more artsy-fartsy flourishes you see on stone-based architecture. If a building is signed, typically the carver is the one who signs it.
Oh, and don't worry about all that Freemason nonsense from earlier. We kid. They're just a simple, kind, charitable, totally not world-dominating organization for normal people like your great-uncle Herb and his buddies to share old war stories. There's really nothing nefarious about it.