So... I've created the wall with packing boxes from OfficeWorks (pk of 10 for $10) painted grey and then sponged with dark grey around the edges- simple. I've made the hanging gardens by poking pieces of green crepe paper streamers into a couple of smaller boxes and resting them on the top of the wall. I did purchase the Tribe posters from Group and mounted them on wooden dowels/wood blocks from Bunnings hardware.
Then, for versatility and to save space, I've printed A3 pages of our various family ministry programs and events and stuck them to the back of the wall boxes to use as a display for children's ministry for the remainder of the week. (See photo below)