We are a private school but anything large scale we present to the principal or church head. If they like the idea, they'll pay for the supplies. They usually like the idea because it's free labor. The men of the school formed a men's club and they've been hard at work doing fix-it jobs. Their thank you? - the principal or church head will have a case of beer and pizza waiting for them. It's a male bonding thing!
On the smaller things, we create a wish list. Someone may donate supplies and then we advertise within the school and ask for volunteers on a certain day to sign up and help.
Does your school have a beautification committee? If yes, what are some of the projects you have undertaken at the school to improve the aesthesics of the campus?
How does your group secure funds for these projects?
What kind of support do you have from the school? Are there teachers or administrators on your team or is all of the work and expenditures on the part of the PTO/PTA and the parents/families of the school community?