Thank you for your re-edit. In fact the two main blocks are: to the SW the combined ticket office/toilet block while the other to the NE is the National Trust shop. As you said you are checking later I will leave the changes to you if you wouldn't mind. I will have look later to better understand how it should look.

Best wishes
Mel

Hi BCNorwich

Thank you for your comment on my edit. I am new to OpenStreetMap so welcome the input.
The building in question is in effect two buildings with a linked roof creating an exposed passageway
through which all visitors must pass. I have added the tag 'tunnel' which I hope should clarify the situation. If you know of a better solution in this case I would welcome your advice.

Best wishes Mel.