Boku no Marie, also known as "My Dear Marie", is a romantic comedy by Takeuchi Sakura. This manga was published in Young Jump and then in at least 10 (to my knowledge) tankouban. There is also a 3 part OVA series based upon it.
Karigari Hiroshi is a total robotics geek/genius who really likes this one girl, Mari. He's too shy to ask her out, so he becomes obsessed with creating a perfect android copy of Mari. He succeeds perfectly in creating Marie, an android with the intelligence and heart/emotions of a human and who looks just like Mari (though with different colored hair). Of course, Karigari never really considered the implications of such a thing...
As far as I can tell from the OVAs and the first tankouban, the story is about Mari, Karigari, and his new-found "sister" Marie's relationships together. The good-hearted Marie tries to get Karigari and Mari together, although she herself has some kind of feelings for him too.
The story is funny, cute, and sweet, at least from what I've seen of it. (Though, I don't personally care for Karigari's somewhat old-fashioned chivalristic view of women.)
BTW, I can't really read Japanese. :( I figured out the first tankouban via knowledge from the OVAs, context, conjecture, and the little bit of Japanese I can make out. I hope someone gets around to writing a translation for the manga.
The front cover of the first tankouban (74Kb). A larger copy is here (213Kb).
Marie looking dejected. ;(
Whoops, she's a little too strong. Next time, don't knock! ^_^;;
Wish Marie was in Philly to stop all those crazy red light runners. ^_^
At least she doesn't have to worry about getting run over.
Karigari's object of affection, Mari (the human one), looking a little confused.