I had debated just adding snow to my existing Pegasus houses, but they were already based for summer and converting the roofs didn't look to easy. I found some nice buildings by Blotz that did just the job. I bought two of each of the three types on offer. It was all going well until I decided to add the snow to the roofs. The wadding I used was very synthetic and wouldn't damp down with PVA, so it ended up far fluffier than I planned. I did debate ripping it off and stating again, but I've got them looking reasonable now.
If I was starting again I think I would use the acrylic sheets dusted with white primer and snow flock as drop-ons over the roofs fixed on with blue-tack or similar