I'm planning to put my home server in my loft. Its just a desktop pc running linux.
Aside from having to put cabling up there (which doesn't concern me) - do you think this is a bad idea? ie. Condensation when its cold or Overheating when its hot. Or even risk of fire ?
I had exactly the same idea, but ended up putting the server in the spare room, in a wardrobe (with an extractor fan!).
The loft just got too hot in the summer, and was quite dusty. Also it would be difficult to get a monitor up there if something went wrong. Basically the problem is that the sun shining on the roof heats that space up so much in the summer, that it would get too hot for any computer to survive.
Intresting, I do think those things you mentioned pose a threat to some extent but I dont ever think I'v see a computer catch on fire. Although the condensation might be a problem to the hardware... I would be cautious about this seeing as I'm not sure where you live or what your loft is like.