Found this site while looking for information on building a room addition under an existing deck. Just getting information before deciding if it is even feasible.
Found some good information here thus far, and may lurk for a while.
I love DIY, and prefer that approach as it really helps with pride in knowing that you did a good job, and did it yourself. So far I have only built my own aquarium stand, a couple raised garden beds, and a large enclosure for the girlfriends bearded dragon.
I worked in framing years back on a condo, and did enjoy it, just not the weather.
Everything I have built thus far has been done with plans and material lists to such a degree that I use nearly everything, and have next to nothing for waste. I always measure three times, cut once.