Joist size.

[pred]

Hi folks, I'm in the process of drawing up plans for a ground floor extension, could someone tell me what size joists and rafters I require please.
The span of the joists from a wall plate to the inner wall will be 3,200mm, the rafters will be about 3,750mm to the outside face of the wall, the angle is quite shallow, somewhere between 15 and 20 degrees.

 

[foxhole]

My kitchen roof was similar, from memory the joists were around 150mm x 50 while roof timber were 190 x 50 [17 degree ]. timber available was usually 47mm .