There is no build world that I know of. The build portals just take you to a place in the wild. Mining world is a PVP/Mining world. There are creepers and the world is pretty much just for mining. (That is why its called Mining World)

 

Yes there are a larger amount of ores in the mining world, but they are placed differently then in the main world

 

To get to the mining worlds you must be a resident ranked user or higher.
Go to our EcoCitycraft spawn area and find the mining portal area near the aether ship!
All mining commands will be listed in our Server Commands section.
Here is some useful information to know about the mining worlds:
PVP is enabled
Griefing is not punishable.
Wars are allowed
Aggressive mobs do not spawn in the mining world. Only passive/peaceful mobs that can be created with ExtCreations do!
Creepers do roam around and will hurt/damage you. Beware!
Weather is fully enabled in the mining worlds
LWC is disabled Get those goods and get back home to store them.
We will not roll anyone back for griefing/destroying/killing in the mining worlds.
The mining worlds are very much alike to the nether. Simply move away from the small protected spawn area, and begin your mining survival adventure!.
No towns/regions will ever be secured for anyone within the mining worlds.
There is a 2000x2000 border currently in effect.
The mining worlds also include a brand new channel accesible with the "/ch mining" command. Alternately you can use the shortcut "/ch m" We ask EVERYONE to keep all chat in the mining channel while in the mining worlds* *Remember however our CHAT RULES are still in place, and our Language rule is still in effect! Do not abuse it or you WILL be punished.
The mining worlds will regenerate once every 1-2 months. Remember dont get too used to living there as we will regenerate the world every now and then.
That's the mining worlds info

 

What do you mean by this?