You need the shelter to be light, strong, weather proof, durable and easily repairable. You need to consider what materials are available locally and whether there are any cultural issues attached. Finally, you need it to be as cost effective as possible.
Broadly, the materials available fall into either stone, brick, concrete, wood, plastic and metal, and most shelters are made up of one or more of these materials. Which is best will depend not only on performance and price, but also on the fundamental decision of whether you choose to manufacture and ship units, or prefer to build them locally.
Each combination has its benefits. For instance, building transitional housing out of concrete or stone means generating work locally, using local materials, is likely to be sustainable (in terms of maintenance), durable, have good security characteristics and should be reasonably cost effective. However, this requires lengthy construction processes, skilled labour, fresh water, foundations, robust equipment and time. All this in an area likely to be short on resources and requiring a large volume of housing as quickly as possible.
Plastics and metal materials are ideal for industrial manufacturing and shipping; the production can be closely controlled and the final design can be reasonably light, offering real benefits for speedy deployment. However, the materials may need to be shipped in from further afield, may cost more, and most importantly, will not be easy to maintain or modify after initial deployment.
Wood based materials, including plain timber, bamboo, plywood, phenolic coated ply, etc. tend to be more flexible. If the material is available locally it can be used to build on site, although the issues of quality control and time (much like stone and concrete) start to become important. It can also be used to produce flat-pack or fold-flat shelters in a factory and shipped to where they’re needed. Although likely to weigh more than the metal/plastic solution, wood is easier to maintain and to repair, offers good thermal characteristics, high durability and security and is more likely to be sensitive to local cultural requirements.
So, what’s the best material to use for transitional shelters? Not surprisingly the answer is ‘it depends’. If you have time and you want to do the work locally, use stone, concrete or timber. If weight and speed of deployment are your key criteria then plastic and metal might provide the answer. If you need sustainable (in all senses), quick and cost-effective then the traditional material of wood will be hard to be beat.