Make a decent enclosure (or for £20 or so buy a kitchen cupboard carcass or similar).

Get a cheap thermostat that can switch-to-cool and an extractor fan (get a 150mm/6", not a 100mm/4")

Use some ducting to get to outside (maybe the soffets? - I hired a core drill and drilled through the wall). Orient the fan to suck air from outside and set a temperature.

Voila - a dust-free, temperature controlled server facility in the attic

You could practically run a chip-fab facility in there....