I'm going to build a conservatory outside our kitchen extension. It
will be a lean-too configuration supported on two sides by the
existing house and will be 4m by 3.5m.

I have two design limitations that I can see at the moment. The first
is that the gutter height of the house is only 2.5m. To overcome the
lack of head room this is going to give, I intend building the frame
of 50mm box section galvanised steel. At the moment I can't see any
problems with that - anybody got any comments?

The second is that the structure will include two bedroom windows and
correspondingly I intend to do the conservatory roof in glass to
reduce the light loss from those rooms.

This is where the questions come!

1 Do I use double glazing and what what weight of glass will that
involve ?
2 I can calculate the structure deflection but what deflection will
the glass tolerate? My current guesstimates of weight show a 2mm
deflection on the 3.5m sloping length of the structure (and that
includes 3" of wet snow).
3 What angle should the roof be at?

Thanks for any help

Rob