This is a model I designed to mount the Unifi brand AC Mesh outdoor wifi access point.  I wanted to mount the AP on the corner of a building but didn't want to add a separate block to achieve this and couldn't find an existing design. 

My building has steel siding so the mount was  screwed using two self-tapping sheet metal screws through a pair of 3/16" diameter holes I drilled in the bracket.  (These holes could obviously also be added to the model.)

For attaching the bracket to the building I first drilled the two holes through the flanges, then I temporarily secured the bracket to the corner trim using double-faced tape. When I was happy with the position I used two self-tapping sheet metal screws.