was asked via pm what dimentions i used for my double free stander. I have always used this plan as the model for all the high seats i have used, the critical dimentions being depth of seat back to rail, rail to top step and height of rail. get these wrong and it can be really uncomfortable to sit in.
for a free stander you have to angle the legs to get a decent width of base but on a lean to it makes more sense from a structural point of view to have the force running longitudinally down the uprights and to try to minimise transverse forces ie the more you slope the ladder the more it flexes. this plan and high seat picture was borrowed from a friend and ive found no reason to change it