Interesting idea.
Possible Logic flow; (No, i won't be working on this)
If ply is in cube coordinates set by admin tool then
If ply is owner of area then
get/store current ply access
raise access in memory only (don't want them to leave/rejoin server as new high access
....
Now, as for how/when to check the players coordinates in relation to the area, in my mind, thats when it starts getting complicated and optimization required.