Guild Wars 2

I have created a new guild and am wondering where and how much it costs to create a guild castle.

There is no “guild castle” in Guildwars 2.
There also isn’t a guild hall or anything alike.

If your server has taken control of a camp, tower, keep or castle in World vs. World you can claim it for your guild and upgrade it.

There’s more info on the general process here: http://wiki.guildwars2.com/wiki/Structure
And the pages for individual structures explain what upgrades can be purchased for them.