Roost restores half of the user's
maximum HP. If the user is a
Flying-type, it will lose its
Flying-type (thus being treated as a
single-type Pokémon) until the next
turn. If a non-Flying-type uses Roost,
then there are no additional
Roost does away with your flying typing the turn it's used, yes. That dynamic punch would then be super effective against skarmory without its flying typing.