We have a sheet steel garden shed, and with any sun at all it gets
unbearably hot inside.

We put up polystryene slabs under the roof, but that was to stop the
condensation dripping down inside in the winter. It does not help with the
problem of the shed getting too hot.

Grateful for any suggestions as to best how to keep it cooler in this warm
weather, please.

Trying to cut out holes in that tin sheeting would I guess be a difficult
task, and I've no idea if it would be of much help? Thanks for any advice.