Due to the nature of mushrooms, washing them can cause them to be waterlogged. If you see any dirt, you can brush the dirt off with a mushroom brush or wipe the mushrooms down with a damp paper towel. If you really must wash them beforehand, you can rinse them with cold water and immediately pat them dry with paper towels. You don’t want the mushrooms to absorb the water as they will get waterlogged and the texture of them won’t be the same when you roast them.