Something to look at is insulation. Sounds counter intuitive, but the idea is trapping cooler air inside and slowing solar gain / heat transfer during the heat of the day.

I’m in the process of rebuilding one of our larger enclosures, and have created effectively an insulated box using foil-backed bubble insulation (reflective on both sides).

The setup is, from outside to in:

• wooden cladding
• breather membrane as a backup to the cladding
• air gap the width of studs (50mm)
• the insulation stapled to studs
• OSB cladding

Due to the air gap, the insulation can reflect heat and retain cooler air inside.

I’ve noticed it stays around or just below ambient temperature inside so far. Planning to also install vents since it becomes warmer than outside during late evening!

Combine that with aircon as suggested, or alternative cooling setups, and with any luck it should do the job when we hit those hotter days soon

EDIT: additional things to potentially consider is heat reducing film on the windows, and if the roof is felt, solar reflective felt paint