Most of my bikes are stored in my loft. I boarded it out a couple of years ago and put in a larger access hatch and ladder.
I just need to remove the front wheel and seatpost to get the bikes in or out, so I can have a 'stored' bike ready to ride in less than 10 minutes.
My loft isn't very large at all, but I think there are about 12 full bikes, a few frames and wheels up there at the moment, along with all the usual xmas decorations/camping stuff/cowboy hats etc...
I've lined the rafters with insulating foam panels, and the temperature fluctuation would be much less than in a shed for example, if I ever get round to building one that is.
Of course the problem with using your loft for storage is that you will inevitably have room for more bikes.
I only had 5 pre loft. Now I'm approaching 20 I think. I've completely lost track of spare parts...