Starting perennials or biennials in the autumn

I sow in modules or pots in the greenhouse and keep them there until Spring when I'll plant them outside if they're big enough. Many seeds with deep dormancy will happily stay outdoors all winter until they germinate in spring. You don't want the pot to get absolutely sodden though. I did this with some rowan seeds last year, kept outside in a hummus container with holes poked in the lid, but out of the rain. A shed would probably work. There is a method where you sow into plastic milk bottles, cut in half but keeping the top connected (lid off) with a thin flap to act as a lid for venting on hot days.