Is it wrong to have a Homosexual orientation? Does a person choose to have a Homosexual orientation or not ? Should someone with a Homosexual orientation try to change their orientation and make themselves into a Heterosexual ? Is it sinful to find men attractive?
Yes, homosexuality is sinful, much in the same way that heterosexuality is sinful.
God's definition of marriage remains a monogamous, respectful and loving relationship between a man and a woman which lasts until death. Any sexual activity outside of that—lust, extramarital sex, what have you—is sinful. In that sense, a homosexual person, a bisexual person, and a heterosexual person are not that different from each other. Each of them may be tempted to sexual sin. The only difference is who they are tempted to sin with. Lusting after the opposite sex is just as wrong as lusting after the same sex.
I don't think it's something chosen anymore than heterosexuality is chosen, and I think trying to understand where sexual orientation comes from in a sense beyond living in a fallen world is a complete waste of time. People are free to disagree with me on that, of course, but I don't find that it's very helpful.
(And for what it's worth, speaking on someone who struggles with same-sex attractions... I didn't choose this. Neither do the other Christians I know who have dealt with this. But for whatever reason, God has seen fit to use our long-term struggles to draw us closer to him.)
I'm not about to say that, upon becoming a Christian, someone will no longer struggle with their sexuality, regardless of their orientation. Lots of Christians continue to struggle with same-sex attractions in the long-term, and choose to abstain from homosexual relationships, activities, and so on as a matter of staying faithful to God. It's not an easy road, but lots of people find joy and peace along the way.
I'm also not about to say that God will not see fit to change someone's desires entirely. That said, I've found such cases are overhyped and extremely rare. (Also, the theological reasoning behind it would require a belief that heterosexual lust is somehow less severe than homosexual lust, which I don't see as rational—even working from a belief that some sins drive you further from God, whether you're an inch away from Him or a mile a way from Him, you're still separated from Him.)
Regardless, I'm not about to argue with someone who claims to be "ex-gay" that it's impossible for them to have experienced orientation change. Maybe that's just how God saw fit to use that person for His glory.