Hi - thank you all for your advice - our Garden shed is new (and empty) and he was the only one in it - we had his kennel, water food etc in there with him.
Poor puppy - he is barking because he is frightened being on his own in a shed.
Is there a reason he can't be inside with you?
He can be inside with us... he just isn't properly housetrained yet and I dont really want to be cleaning up wee/poo all the time. The times we do have him inside with us (before we all go to bed) I always take him out regularly to go to the toilet but he occasionally has an accident. I'm worried that he wont ever learn to go outside to the toilet.