The OEMs get parts for a whole lot less than you can (look at some of the deals offered by bikesdirect and others). You may be able to find specific parts at a bargain but then you may end up with a Frankenbike. Although you'll want to sell the bike as new, there's no warranty, no support, no free tune-ups so don't expect buyers eager to pay full retail. Remember, they are looking for bargains too
I agree with DaveG. You may have put together a bike for 1500 that you think should have had an MSRP of 4400 dollars, but nobody buys a bike for MSRP unless it's ultra boutique/custom. So your 4400 dollar bike is probably 3800 from a shop. That shop assembles it professionally and takes care of it, but even more importantly can provide warranty support for the new (in the eyes of the manufacturers, which is what matters) parts and frame. Without warranty support, a bike that sells for 3800 dollars new can't be expected to be worth more than about 2 grand on the used market, even in like-new condition.
So, that means you might be able to sell a bike that you put together for 1500 dollars for 2000 dollars. But that's assuming your initial cost estimates were correct and not optimistic on one or both ends. Does your 1500 dollars include all the time it took you, and the cost of shipping all of those small parts? If you've considered all of this and you still think you can make a profit, good luck. And even if you barely break even, it can be fun building bikes. Lord knows even shop employees aren't in it for the money per se. I don't mean to throw a wet blanket on your fun, I'm just relaying my thoughts based on so many people I've seen who can't get half of what they think they should for their used gear.