I've made male and female avs, even tho I'm female, cause I just love making avs. What I usually do is start with a good complete avatar. Usually what you wind up with is the body and a notecard that comes with it that tells you exactly where to get the right skin and hair and exactly which skin and hair to buy to get the exact avatar look you have bought. I try to buy the ones you can modify because you can change some of the features on those if you want. If it's non modify you are stuck with it the way it is. I find the best ones without shopping all over second life on the marketplace (just click on the "shopping" option above and click on "marketplace" and you're there. Then go to the category on the left "avatar appearance" and from there select "complete avatars". Now you can choose the human male category and you'll find pages and pages of choices). My personal preference are the avatars from NOON. Put that name in the little search field and their avs will come up. They are pricey and so are the recommended skins you have to buy after you get the body. The body gives you the facial features you need to go with the skin for the right overall look. And frankly you get what you pay for. You can get cheaper ones made by other creators and they're not bad, but you won't get the muscle definition or six pack look. It will look more flat like skin colored latex. Once you've got the body, you can make it more slender if you prefer or shorter or taller, but don't make the mistake of turning it into a hercules. Newbies always do that and the incredible hulk look is a dead giveaway that you are a clueless newb.
So that's my advice. There is a service called "pimp my avie". That's the only one I know of. I've seen some avies of theirs and they're good. You can find them if you do a general search in the search function. They are probably pricey too. As much as the prefab complete avs I mentioned above or more, so your choice. Good luck.