a link for information on outposts is http://mow.wikia.com/wiki/Outpost
it sounds like you are trying to build an outpost in a CZ your guild DOES NOT CONTROL. Either that, or your guild leader never gave permission for you to build an outpost. I am not sure, but it might be possible for a different guild to give you permission to build in their CZ, but why would they?
I don't know if you can still take over outposts. if you try it, bring at least 40 catapults (the town center has 100,000 hp, so you want something that will do some damage). you can store your army in a nearby lair between attacks. You no longer gain loyalty for building walls/towers/gates, but they can still donate gold once a day to bring back loyalty (10,000 gold per point)