Doing the work yourself can save you money. This is one of those statements that can hold true 2 ways. For some people, doing home renovations yourself can save you money. This is true IF you have experience and know what you are doing. Th opposite is true for people who attempt a project with limited knowledge and in the end have to hire a contractor to fix mistakes. In the end, the project cost has greatly increased.
There are also the long term maintenance costs to consider. You may have been successful as adding a room that looks well done but what if you fail to properly insulate the room? Over the long term, you are paying extra for that renovation through things like increased heating costs.