The strength of wood is that it is easily worked with common tools, it is inexpensive and holds together well when well designed. It is a project anyone handy could handle with little or no help. It isn't hard to design a structure that will stay together and erect with wood.

Its weakness is that it is hard to design in enough resistance to penetration to meet the forces involved with 2by4s coming end-on at high speed. A partial solution is to incorporate some sheet steel to boost resistance to penetration but the protection is not often complete and it both raises the price and difficulty of the construction process. Locating the room well inside a structure also helps as anything that would strike the room has to get through the rest of the house first.

Most commonly approved designs use a lot of poured concrete, usually in the form of concrete blocks with filled cells or expanded styrene forms, and rebar to hold it all together. The down side of this is that mixing and pouring concrete is labor intensive. Commercial mix trucks, or short-batch mixers, and pumping greatly reduces labor but pouring in an existing structure can be complicated and it is often more than a home handyman is comfortable doing even with help. Pumping and vibrating a yard or three of concrete is a job for at least three healthy people.

An experienced commercial concrete crew can set up and pour a small room in a couple of days so what they cost you might be offset with savings in time.

There is another form of concrete work, tilt-up panels, that can be worked by a couple of carpenters using concrete delivery trough-fed right off the truck. These wall and ceiling sections are laid out on flat ground or slab where the truck can get to them, formed up and the rebar and mesh is positioned like you would pouring a slab. After pouring and finishing the concrete is allowed to come up to strength and then the slabs are tilted up and shifted into position, and joined.