Here's a good shot of the stair tread
fastened to the stair stringers, with the upper and lower rounded nailer,
ready for the plywood strips to create the round riser.
It's always a good idea to cut the length of your plywood strips, with
the grain of the plywood. Cutting them in the opposite direction could
create a weaker round riser.
If you're looking for some additional strength, it
wouldn't be a bad idea to apply a good construction adhesive to the
round nailers, before applying the plywood risers strips. Sometimes I've
even applied the construction adhesive after I'm done building the
Split Level Stair Framing