Another Note: If you plan to take over or vassal Graygarden, do NOT be surprised if the settler you have to talk to is on top of the stupid town on the highway in an unreachable location;When i built up Graygarden i built the settlement into the overpass, so settlers don't have any issues with spawning on the top. It's basically a nine floor arcology composed mostly of concrete and turrets. i even placed the artillery on top of the overpass, the ground level is mostly farming space.
Build some stairs up to the top of the highway first, because Bugfesda decided that on top of the highway in an unreachable location was a good spot for idiot settlers to spawn even if there was no possible way for them to get there. I was effectively forced to use the command console just to talk to the idiots when I decided to vassal them.
When i built up Graygarden i built the settlement into the overpass, so settlers don't have any issues with spawning on the top. It's basically a nine floor arcology composed mostly of concrete and turrets. i even placed the artillery on top of the overpass, the ground level is mostly farming space.
Also, something i didn't do was dismantle most of the settlements' defenses before doing my heel turn. In retrospect that wasn't ideal since settlements with over 300 defense rating due to turrets everywhere can be something of a PITA to subdue when most of the residents are equipped with assorted automatic weapons and combat armor.