Ravenwood - Andrew Peters

Fourteen year-old Ark has the squittiest job on Arborium, the last
forested island in the future. A poor plumber's boy, he unblocks
toilets in the city where he lives - a breath-taking, mile-high
world carved out of the vast upper branches of a giant canopy of
trees.
Protected by a poisonous shield, he believes his forest kingdom to
be the safest place on earth. But while at work, he over hears
a plot between a powerful councillor of the island and a secret spy
from Maw, a superpower of glass and steel, that intends robbing
Arborium of its wood, a natural resource now more precious than
gold.
Ark is plunged into danger and soon he finds himself on the run,
fighting for his life. Together with new found friends, he must travel
from the highest tree-tops to the darkest roots of Ravenwood
to save his home and his people.