[OldGaffer]

Just done a search and so you can, the large polytunnels look impressive with doors to the side. I stand corrected 

[kate7590]

Yes they're made especially for sheep so ventilation isn't an issue.
Our home made shelter was destroyed in the winds and posts that were over 2ft in the ground were ripped out, so we are not going down that route again.

Going to try and order it soon as my poor sheep are cold….. Thanks to those who helped with my measurement issues