New shed, 4m span, timber or steel framed?

[CallumA]

its a home made design but based on a king post truss and was going to be a sissor truss but I thought the parrallel 8x8 and 6x8 would be strong enough (plus too many angles to workout)! it wont be sitting on the walls inside the shed i will have 5 x 12x12 posts each side and a 12x12 top plate with 6x6 braces and braced onto the trusses so hopefully it stays square! the roof will be box profile, the notches on the rafter are for 3x6 purlins. Hope to get it up this year but the wife may think the funds are needed for something else!