We decided to build mainly because we could get things exactly the way we wanted. Ours is not a custom build, but we are building with a very large builder for our area and therefore the prices were very much in line with or cheaper than what we could buy an older home for. our loan is an FHA loan and our lot came w/ the house, it was a "package deal".
I think many times people don't build is that they don't even know how affordable it can be, and also it's associated with a lot of stress. I've heard people (including my own parents) say how stressful it is to build and that they'd never do it again--yet they have!. I think it really depends on who your builder is , whether it's a smooth or bumpy ride. There is always going to be minor hiccups but as I tell my husband that happens even when purchasing an old home! I know for my husband this has been very hard. He is a perfectionist and looks at the home down to details that most would not. I haven't yet decided if this is a good or bad thing. 
But it can be stressful for him if things don't go exactly the way he thinks they should!
So it's really whatever your preference is. I would reccomend at least talking some builders in your area and really sitting down and comparing the cost. For us, that is what sold us on the idea to build and customize our home. Hoping to close on it in a few weeks!!
I asked this same question myself a few months ago.
it comes down to preference. Example in my case I am a single woman most home in my price range were 15 or more years old. (just about the time big things start breaking etc) I did go look at resales. Saw a few I liked but saw a new build where I just absolutely fell in love with the floor plan. So in my case I decided new cause there will be a waranty on everything. I was able to pick all the finishes. So I shouldn't have to worry about major issue for many more years.
What I lost by doing this was a larger yard. If I had children I would have had an issue with this and would have not gone with the new build that I did.
So it is personal preference basically.
It just depends on your preference. I have stayed in and owned an older home...and the headache that comes with repairs(once you open the walls, floors, older pipes etc) can get pretty pricey. With newer developments you can select your floorplan and make the decisions as to what carpet, tile, etc you want. Plus there's warranties involved. Purchasing an older home, you may not always be covered under a "home shield" program with major repairs. We needed a furnace replaced shortly after moving into a house, even though it "passed" inspection before closing. AHS told me they wont replace bc we "failed" to maintain it...how can you maintain an existing furnace after just moving in??
The newer developments, especially if you do their in-house financing, offer great incentives and alot of times throw in upgrades if you can get into a neighborhood before the development closes. So you can just guess which option we're going with next, right? LOL
Starting Score: 503
This is a very good question. I've always thought of it as a personal preference and never was able to convince myself nor the husband on building new. We prefer established neighborhoods/neighbors, we can't afford the expensive upgrades that are involved with a build, we love the "character" that an older home has, and we usually are too impatient to wait for a build. We have never purchased anything built prior to the 1980's. In my experience of purchasing a home that is a little over a year old, I've found that the particular builder poorly built their homes for quick sale. The foundation, insulation and heat/cool systems were just not up to par.
I have never considered the point re: energy savings that ezdriver made though. Something for us to think about on our next purchase. 
@physicist82 wrote:We decided to buy a previously built house because the new houses in our area carry with them a $90 or more HOA fee. They also have miniscule tiny yards. I'm talking .10 acres being the biggest. We have 2 kids that love outside and are very energetic and a dog so this was a deal breaker for us.
The house we got was built in 98 and has .25 acres. It's also not situated right behind the auto zone where you are looking at the rooves of businesses from your 2nd story window.
I also feel like some newer construction just isn't as good a quality as it was even a decade ago. My grandmother's house has stood for 60 years but the house we are renting that is only 8 years old is falling apart. The 1998 house we are buying is in better constructional condition then the newer house built in 2006, and they are only 3 blocks apart from each other.
This is also true. If you go with a new consrtuction make sure its by a well reputable one. Check the BBB for any construction complaints. There's companies that are literally slapping up homes. If you can visit your property while they are constructing, visit the property OFTEN. If you have a best bud that's also a contractor...bring him along too!