SC2Mapster

Personally I'd separate this into 2 triggers.

using a Global array of size 12

The first based of Unit uses ability (Build)

Actions

If Unit = X

Set var Global Array [Owner of (Triggering Unit) = X (number that you decide represent that unit)

---

Then on your Every 30 second Script

Every 30 seconds

For every intA from 1 to 12 increasing by 1 do
if Global Array[intA] == X
Then
Create unit at X region.

This will ensure if you have a lot of checks it doesn't cause the game to freeze up.