At our VBS this year we decorated the building like a Jungle. We used the large cardboard tubes that are the core of carpet rolls. We cut strips of brown paper about 9-12 inches wide and wrapped the tubes (overlapping the wrap by 2 inches each wrap) Then we "pulled back" on the overlapped wrap. This gave a palm tree bark effect. Next we cut large palm shaped leafs from green rolls of paper and stapled them to the top of the trees. We placed them on 2 X 4 stands in small bunches around the building and strung vines everywhere with blow up monkeys and birds everywhere. It looked GREAT! And it was very inexpensive.
Good luck with your project.