To the Rooftops requires you to Complete all Area 2 levels on any difficulty setting. Earning this achievement unlocks the Landscaped Crystal Skin.
Area 2 levels are listed as the second levels after the first boss and including the second boss.
The Body of The Beast - Completed all Area 2 levels on Hard
Through The Crowded Keep - Completed all Area 2 levels on Insane
Team Effort - Completed all levels with 4 active players on >= Medium Difficulty