Banana leaves do die off so there may be nothing wrong. Can you see a new leaf forming in the centre? If it has been outside during the summer I would inspect the roots as I have had vine weevil grubs eating the roots of mine in the past.
A remote control to turn the sun on
You may find it's cheaper if you buy from a packaging company instead of a GC. I got mine a couple of years back from Staples.
Geoff, Hampshire half term is next week
Mine arrived today.
I find that the bees like any dahlia where the centre is open. So they would like the white ones in the photo, but it's not clear with the purple ones. Earwigs would like them as well
Clay shrinks and expands a lot so probably not the best stuff to have beneath a patio as this would rise and fall leading to cracks. It would also be hard to compact the hardcore if it was sitting on recently dug clay.
I didn't realise that there was something called a "legal Garder Designer". There must be a governing body that oversees registration so maybe they could help. Just flick thru our local mag and none of the adverts for garden design give an indication that they are trained or legal.
Why not start with looking at the Royal Horticultural Society website as they do plenty of courses and recommend others. www.rhs.org.uk
I keep mine wrapped in fleece in an unheated greenhouse so would expect it to be OK in your summerhouse. I did lose the leaves one year but the plant regrew from the base so probably hardier than we think.