I've installed awesome as my windows manager. However, it doesn't seem to respect the power options from lightdm; if I'm at the login screen shutting the lid will trigger suspend.
Once I log into the awesome wm, however, this no longer happens.
It no longer happens because power management is different between lightdm and the the session you log in to. Each session is expected to handle its own power management, for various reasons, and so you will need to run a power manager with your WM to get this feature to work as you wish.
A good power manager for the task would be