Hi, I'm building a garden workshop/shed (4.8m x 4m) out of 150mm block. At the front (the 4.8m side) I have door with a window either side of it. The windows are softwood frames with uPVC windows in them; they are each 1100mm wide. The door has a hardwood frame 910mm wide giving a span of 3110mm. I am going to put a pitched roof on this of about 25 degrees using concrete roof tiles. There will not be any block work above the door or windows but it will be supporting the roof. My question is do I need a RSJ above the door &windows or would a length of 4x2 do instead? Thanks.