So.....who's doing what in the way of 3D printing for T gauge???
I'll start off.....
I have designed quite a lot of the components for Robins Run. The brick viaduct and large concrete bridge were printed by (I think) 3DPrintUK to my own design. All the tunnels and liners were printed by Shapeways (& are available in my shop there).
Since getting these items made, I've invested in a 3D printer (Makerbot Replicator 2) and have produced quite a lot of items: houses, cottages, platforms, a couple of outbuildings, a three track footbridge similar to the superb brass bridge available from TGauge.com. I've also produced a range of Mk 1 carriages and a Class 25 (Baby Deltic) loco shell that I had available for sale from a web site until I took it down to make way for this forum.
Now I've got Robin Run nearly complete, I may take a fresh look at the array of items I've designed...and make some available to purchase at reasonable prices to help fund the forum's future.
I use a little known 3D package by the name of 3DCrafter (available from Amabilis.com) that I've been using for many years..which I find very easy to use compared with some of the other free/budget packages. To get the right file format for the printer software ( .stl format), I export as .3DS format and then use NettFab to check and convert to .stl format. This arrangement is fine bu for the niggle that 3DCrafter errors after every time I export to .3DS format.....the export is perfect, but the program gives a script error, and then half the time exits. This isn't a problem....as I usually am finished with 3DCrafter at that point.

When I was using Shapeways to print items as I developed them, I found that the development of individual items was very slow and quite expensive. You create an initial design, upload it, pay for a few prints, wait around 10 days for the prints to arrive.....and then find the item is not quite right, and the cycle is repeated!! With my own printer, I can run through the complete design phase in as little as one evening, having produced two or three sample prints! Beleive me, its makes the whole process really enjoyable.
One BIG word of warning....the extrusion 3D method does have some dimensional and detail resolution limitations when compared with the processes used at Shapeways. But there are advantages...such as the PLA I use is far, far stronger than the FUD material. This makes you have to design for the printer as well as for the item you are making.