Photos as requested.
I must say, having looked at these, as it were, from a fresh angle, I now think the terrace is too small and narrow to have one of the big cantilever angled umbrellas I was hankering over. It's also used as a walkway from the side of the house down to the front garden as OH occasionally takes the lawnmower down that way. I'm not sure I could persuade him a pergola is the way to go either, although the wisteria could be trained up and over it. The terrace itself is hollow underneath as it was originally built as a coal store, although unfortunately not high enough to stand upright in it.