Honestly I'm not expecting Roma to lose tomorrow. Most people would favour Leverkusen but I still think Roma won't lose home in the 1st leg. De Rossi's arrival has started to change things for Roma. They are stronger and especially in home matches I have really liked their performance so far. Even against Xabi Alonso's team I think De Rossi won't be losing already.
But for the second leg I wouldn't have the same opinion. I already favour Leverkusen to advance to the final. But I just expect a tough challenge before that.

There's a possibility Roma will lose, just like Bologna humiliating Roma in Stadio Olimpico. Bologna is a rising star team similar to Leverkusen, it's either Roma will lose or draw, high unlikely they will beat Leverkusen when they always evade to lose.
Roma lost Lukaku in this match, Dybala will be easily get destroyed since he has glass leg.
I'm convinced Leverkusen will win in this match.
This is a home match for AS Roma, so they can take advantage of this match to achieve a victory in order to widen their chances when competing in the second leg. Considering that their opponent is Leverkusen, Leverkusen is a team that is doing very well this season, this will not be an easy task for them. Leverkusen is also targeting champions in the Europa League, because they no longer have the burden of the Bundesliga, so they can focus more on matches in the Europa League.
If Leverkusen can win, then they will be more comfortable when playing in the second leg, because they will be playing in front of their own supporters, and we know that Leverkusen fans are very enthusiastic this season.