Have you thought of using either twin walled or triple walled poly carb?
It has a built in strength and a lot less weight than glass so requires a
lot fewer glazing bars, It will give you very good insulation, and is
unbreakable under most circumstances.
Whilst the initial cost is more than glass the extra is soon recovered by
the saving in heating costs.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk