what are they building at the min
I'm not sure, but those photos above show the wall around the coaster section of the ride. The two lower sections at the front are were the track will enter and exit this part of the showbuilding.
So will the showbuilding be called "Studio 4" then? That's good, I'm glad to see them continuing the numbering system.
One strange thing about Crush's Turtle Twister is that we still don't really know what the finished building will look like. Will it look like a mini Disney Studio 1? Or perhaps a slightly altered Disney Studio 2/3? The main concept art shows it as a grey, industrial building with an arching/curved roof. (check back a few pages if you haven't seen it)
Which design would you prefer?
I think I'd like the one from the concept art, because it looks interesting and is different to anything else in the park. Having a DS 1 lookalike would really turn the park into a collection of yellow buildings... I can understand people disliking the industrial design though. It looks good with the blue undersea facade though, and it might be good to have something that looks weathered in the park - it all looks a bit too modern at the moment.