Want a romance drama where the mc is perfect and by perfect I mean he is calm and cool. An example is the mc from my love from the star. 

Love O2O - It is a chinese drama and it's about gaming. The male lead is exactly like what you explained. 
I see So Ji Sub that way in Oh My Venus
Across the ocean to see you
Goblin - He is calm and cool when the girl is around :)
Another Miss Oh - a bit more broody maybe than calm but still pretty cool
Descendants of the sun - confident, cool and calm even if all hell breaks loose but a bit more on the joking side 
Tomorrow with you - surely confident and calm but maybe a bit too calm at some points?
Queen In Hyun's man - definitive calm and cool and at least half the drama does play in a modern setting....the other half not - time slip
(Moonlight drawn by coulds -not a modern setting but I will still mention it, because it's an easier watch than many other saeguks and the lead fits the description, although he is also very kind)
She was pretty - cool and calm but a bit of a jerk, took me a second try to win me over - first i was rooting for the second male lead. Maybe watch this one when you have taken a liking to the actor Park Seo Joon in other projects, then it will be a lot easier to root for him in this one as well
I remember you - calm and cool and pretty perfect but also very focused on his job, not as much romance in this one
W - perfect as in created to be perfect
Doctors - calm and ...cool maybe, I guess. He could fit but he is her teacher first, so there is some authority mixed into his demeanor. 


My Amazing Boyfriend (chinese) - if you like chinese dramas then definitely give this one a try. Many say it's copying My Love from another star but I wouldn't compare the 2, just enjoy them as their own thing.