There's already a thread on this with sound clips, pricing, etc.
http://www.golfmk7.com/forums/showthread.php?t=15280&highlight=Muffler+delete
The issues is to build one for a 1.8T golf and know it'll fit properly id need the car. I have no way of knowing how similar the routing is to a gti. Once I built one local I could build a jig but there's so small of a market for the 1.8T other than just changing the size of the reducer to fit the 2.25" golf vs the 2.5" gti I couldn't justify it.
Gti dual muffler delete would be $440ish, $780-800ish for a full dual cat back. I've only built and fully priced out single exits so far.
Like I said before tho I haven't built a jig yet so locals only at this point other than the single muffler delete I currently have for sale.
I personally don't like duals on a four cylinder car, but that's just me. From a price stand point it's a ton of extra time and money building unnecessary duals.