There are lots of waffle stitch hat patterns out there, but most of them do not use the pattern stitch for the shaping at the top. This pattern is worked from the bottom up, with a built in folded brim, and the decreases worked in pattern. If you are comfortable seeing your stitches and with post stitches, it shouldn't be too difficult.
I love how waffle stitch creates a strong, all-over pattern, but is still sufficiently understated to be unisex or to pair with variegated yarns. This pattern includes instructions for infant, child, and adult sizes.