Pete
Ask for a lot more photos for starters (before deciding to go and see it). I personally find it a bit strange that it's being advertised before it's finished so you don't know what your going to get after you've paid your money. I don't know the company selling it but no doubt the Staffordshire / Cheshire folks on here will.
If you do go and see it get somebody who knows earlybays to go with you. Maybe someone on here will volunteer! (If I still lived up that way I would offer).
Ask them for photos of what it looked like before it was painted. A lot of US imports more recently can have rust and rot issues and it is rare to find a really solid dry import now.
Hope this helps, Good Luck
Andy