I think that this poster is well made for its target audience, it uses bright eye catching shades of blue and a familiar layout to Facebook a website many people recognize. I think the layout of the information is good, there isn;t too much writing so it is much easier to read.
Concept: putting a vine, eg passion fruit, choko, etc over the garden shed to cool it in summer and make use of the vertical space for food production, plus it looks more appealing. Could even grow different vines at same time to add greater visual and food interest. Plus, Great book, apparently ;-). All you need to know about how to build your own little green roof on a shed or outbuilding.