Paizo has posted the Building Creatures and Building Hazards sections from chapter 2 of the upcoming Gamemastery Guide for free download.
"As we’ve noted on some of our livestreams, the system for creating your own monsters and NPCs uses a top down system with benchmarks, allowing you to build a creature to match your top-level vision of that creature instead of requiring you to build them from the bottom up like a player character. This guide has all the relevant numbers for creating these creatures, as well as lessons on what you can do to make your monsters the best they can be. The numbers are a starting place, and your creativity really brings the monster to life. The hazard rules give you everything you need to create traps, environmental hazards, and haunts to menace your party."
"As we’ve noted on some of our livestreams, the system for creating your own monsters and NPCs uses a top down system with benchmarks, allowing you to build a creature to match your top-level vision of that creature instead of requiring you to build them from the bottom up like a player character. This guide has all the relevant numbers for creating these creatures, as well as lessons on what you can do to make your monsters the best they can be. The numbers are a starting place, and your creativity really brings the monster to life. The hazard rules give you everything you need to create traps, environmental hazards, and haunts to menace your party."