well its so easy to build an NPC Garden..
the level of npc is depends on the flat valley u attack.. in short if the flat valley is level 4 , make it city then abandon it and it will become lvl 4 NPC... the Level of valley Change every Server Maintenance except if u already owned that valley..
if u targeting lvl 5 Npc then attack only lvl 5 flat valleys.. for the other flat valleys that not level 5 just wait the maintenance..
Also u Can make it fast if u have more vacant cities.. u can make it as many as u can..
PS: it may take days to Build an NPC Garden..
HOPE it can HeLp..
`PINOYz - Jhenny