i would say that it depends what you want to spend mate,anything from oak or something downwards really m8.
i would probly use a softwood tho,seein as its an outhouse and not on the front of ur house in full view as a feature. i would recommend using a decent pressure treated softwood tho,otherwise theyl rot in time (although all wood would given all the time in the world) maybe a simple 3"x1" ledged and braced type arrangement overclad with matchboard and then treated with something the colour you want them.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!