Hmmm, might copy the curved sleeper stairs at the rental.
They are a little complicated… the maths is simple enough, when you know the outer radius of the stair, calculate the perimeter of a circle of that radius, and divide by 200mm to get the number of sleepers that will fit around the perimeter, then calculate the perimeter of a circle 1200 less (or the width of the stair) and divide by the number of sleepers - this will give you the width of the sleeper at the narrow end.
All you have to do is rip the resulting wedge of each sleeper (in my case 17mm) and look what happens!
Because I only want to do it once, I didn’t lay them on the ground either (they are H3), I used H4 fence posts as joists and bits of old water pipe as posts bolted to the joists. Beneath them is excavated to keep the bearers above the ground.
They look good though.