Going to put up a lean to shed for logs. Floor Area will be 15'9" ×15'9". The height will be 10ft high (front) sloping to 8ft (back). That's a 2ft fall. I intend to use 6x3 timbers. Question:: 1. what size RSJ's for the 4 uprights. 2. Should I use 2x RSJ' to carry the timbers for the roof and if so what size. I will probably sheet the 2 sides and back down to within 2 ft from the floor and keep front open (for now anyway). It will be in a shaded place with little or no effect from the elements. Just clarification on the RSJ sizes please.