My daughter wanted the perfect slouchy. It is a very simple pattern, but seems to be a success as she hardly takes it off! You can use a heavy worsted to Aran weight single or combine two fingering to sport weights. It's a very forgiving pattern but generally the lighter weight the yarn the slouchier your hat will be.
General knitting skills.
small (medium, large)
20 (22, 24)" head
Change needle size if necessary to obtain correct gauge.
16 sts = 4" (row gauge not important) in stitch pattern with US 10 needles. This is measured unstretched. Swatch stretches easily to 12 sts = 4".