Hmm you're right about maintenance. Ventilation shouldn't be a problem I'm planning on building some vent slides into the coop. This is England so they'll be lucky for a non windy day anyway!
If you build it too close to the fence or other building that fence/building traps the air and prevents proper ventilation of the area, best to give in some airspace all around it so it can breath...
And that goes hand in hand with maintenance, if you build it too close the small area between the two walls has a high probability of trapping moisture and causing, mold, mildew and promoting rot due to lack of sun light and proper air exchanges...