A guest will have hard time in a home away match and Roma will be the host in this match. They can use their two matches with Leverkusen last season as own lessons and take them as one of their preparations for this match. Leverkusen didn't have too many changes in their players since last season so even they upgraded themselves a lot, there will be some common things with the past season.
Leverkusen must play very carefully and avoid mistakes like in their match with Qarabag FK because Roma are at a higher level than Qarabag FK and can beat Leverkusen and won't allow Leverkusen to equalize the match easily.
At least it affects playing away but if the team has a strong mentality I don't think it's a big problem and so far Leverkusen is a team that has proven that they have a strong mentality, Leverkusen is a team that is unbeaten this season in all competitions.
Leverkusen, who will play away in the first leg, will of course make a strategy to make it easier for them in the second leg. I think a draw is good enough for Leverkusen if they can get it and try to play optimally in the second leg at home.
The point is that both teams must be able to minimize their mistakes as little as possible, no matter whether it is an away match or a home match. Because even if they play at home but their game is not good or often makes unnecessary mistakes, then that will be detrimental to them, because the opponent might be able to use that to their advantage.
AS Roma will have an advantage in this first leg because they will play as hosts, but keep in mind that their opponent is Leverkusen, which is a team that has not been defeated so far. So it is a difficult task for them to win.
De Rossi must be able to see Leverkusen's strengths this season, so that he can implement a strategy that can kill the movements that are the mainstay of Leverkusen's game. It is a coach's job to formulate strategies and the players must be able to implement the strategies given by the coach well, so that they can get maximum results.