Download a copy of super beam if you are sure you can do this yourself. Deflection limits of typically 1/200 will give you what you need.

Don't forget snow load!

I've looked at super beam but to be honest, it's still beyond me. I've seen a thread

http://www.greentram.com/forums/showthread.php?t=1950
that says it's a GIGO program (garbage in, garbage out) and that it's really to streamline long-hand calculations.

Reading back my notes, which look foreign to me even though I did them, I'd calculated the roof area to be either 38.8m2 or 32m2. The reason being was that I read that you only take the direct vertical load rather than the actual area of the roof which includes the pitch. With this in mind I'd come to he conclusion that 32m2 equated to 0.9375kN/m2 and with a 1.5kN/m2 snow load would mean that I would have 2.4kN/m2 loading. Each pillar would then (rounded up) have a load of 20kN which would also be the point load for the beam.

Does this sound right or am I a million miles away?

Crudely then shows formulas for bending, shear and deflection.

Bending for point loads was BM=WL/4

Distributed loads was BM=WL/b

So for a 4700 beam the distributed load would be W - total load (20kN but 2.5kN/m2) x span (4.7m) = 11.75/8 = 1.469kNm

Then,

Z=M/f

So (this is where it's not explained to me)

Z, section/elastic modulus

M, movement or resistance (max bending moment)

f, fibre stress of the material (normal 165N/mm2)

Z = 1.496 x 10(6) why this number I don't know = 14960000/165 = 90666.66 or 90.7cm

So looking at BS 4.1 the steel would be - 152x89x16

Does this all sound right so far?