Generally speaking, Roost is better in more situations.
If this is an in-game scenario, having the option to heal on Gliscor is great as it provides two natural immunities to the team, those being Ground and Electric, as well as useful resistances to other types. Gliscor can therefore Roost on common Pokemon that don't have any meaningful method of damaging it, such as most Electric types, as their level up moveset usually doesn't contain much more than Electric- and Normal-type moves. Because Gliscor is a Ground type, you can easily slot another Flying type on the team without fear of an Electric weakness overlap; this Pokemon can give you your Flying STAB, if you so desire.
In a competitive setting, Roost is definitely better. As a defensive Pokemon, Gliscor would appreciate staying alive and tanking hits for its team, potentially spreading Toxic and/or hazards. Therefore, Roost is a viable option to pair alongside Poison Heal healing. Gliscor commonly uses Earthquake as its only STAB move, as Ground STAB hits a wide range of Pokemon from Tyranitar to Heatran while having more base power than any of its Flying STAB alternatives. Aerial Ace's 60 Base Power, Gliscor's mediocre 95 Attack, and its role as a defensive Pokemon means that it's not going to be doing much damage anyways. The same can be said about Dual Wingbeat; even though it is an upgrade in Base Power, it still doesn't match up to Earthquake's 100 BP, and Flying isn't the best offensive STAB anyways.
