We totally get it. Doing some things on your own saves money. However, when it comes to building a major addition to your home, all you DIYers out there should really think twice. Building your own deck may appear to save you money but if it is done incorrectly, you will incur the expense of having to do it all over again. Or you will have the additional expense of constantly having to repair and correct flaws that should have never been made in the first place. In fact, DIY deck builders commonly make mistakes that the professionals simply do not. Here are just a few.