No, no, no, good god no........
Don't do it, really and seriously, don't do it.
(OK maybe going OTT a little but), If your loft space gets as hot as the last house we had then no, it will get hot enough to warp and destroy any kits, it'll make any paints useless and most other liquids too I should think.
The temperature in summer was horrendous, the roof space, (which was huge i'll add), soaked up the heat from the day and was like an oven.
To give you an idea of the damage that can occur, my wife recently bought a wired alarm system from an ebay seller who'd had it stored unused in his loft for a year, upon opening the box the plastic alarm box which sits on the outer wall was so badly warped it could have been designed as an action man rocking hammock. That was incredibly thick plastic too.
Ideally you need somewhere cool and dark (and dry naturally), if you are using a spare room you could get some slot together shelving racks, and store the kits on those side on like a bookshelf?