Its just a shed. Surely its not been there very long. I don't remember it being there when the land was owned by Finnegans restaurant in the 80s. The car park area it sits on the corner of was just gravel if I remember rightly. It was used as a play area for mini electric quad bikes for the kids. you had to put 10p in the slot on the side to have a go. One of them was annoyingly faster than the other.
I was however very young at the time so it is possible that the joy of playing on the battery powered bikes was enough to make me not notice the Cafe sitting there in the corner.
Sorry that was probably no use to you at all.