If you're buying a new construction home, have it inspected by a private home inspector.
I could wax on and on about how important home inspections are for new construction, especially if the builder tells you that a private home inspection isn't necessary, but I've found that photos are far more convincing than anything I could say. I took all of the photos below at homes in Minnesota that were either new construction or only a couple years old; the issues that you're seeing are all 'original' issues; they weren't created after the homes passed their final inspections by the city.
Click on any of the photos for a larger version.
Roofs
The first thing that I typically inspect is the roof lines - I start doing this as I drive up to a house. When valleys dump next to a wall, or even worse, in to the back side of brick veneer siding, you're asking for trouble. These roofs are designed to fail.
I took the photo above at a house that was almost ten years old. Thankfully there was a small portion of unfinished basement where I was able to pull the fiberglass insulation away from the rim space to confirm my suspicions; this had been leaking for a long time. I really wanted to know what it looked like behind the siding... but my home inspections aren't invasive or destructive so I couldn't get all 'Mike Holmes' on the house (tear open walls, make angry faces, etc.).
Decks
I've written several blogs about deck construction defects, but unfortunately handy homeowners and weekend warriors don't have the market cornered when it comes to sloppy workmanship. Yes, I find plenty of deck defects even on new construction.
The most common deck defect that I find is improper nails used on joist hangers. The nail I'm holding in the photo below isn't even half as long as it should be. I seem to find this defect at just about every other deck inspection.
When special / non-standard joist hangers are needed, there's about a 20% chance that the installer will use whatever happens to be in their truck. In other words, this is usually done right, but I still find a lot that are done wrong. The joist hangers shown below were the wrong ones for the job and won't hold what they're supposed to.