A frost hardy and tolerant succulent that will grow anywhere with a handful of soil and not too much water.  This one has survived two years on a shady balcony but they do enjoy some sunshine.  Traditionally grown on tile roofs in many European countries, houseleeks are said to protect a house from lightning.  My guess is that they won’t grow on roofs in the kind of open, exposed site that is prone to lightning strikes so if your houseleek is happy on the roof you probably don’t need to worry about lightning.