I am the type that would wing it. If you want a lacy crochet cap I would make chain 5 (arbitrary number), join in a circle. then increase by working 2 sts into the previous round. Continue in that manner until it gets big enough. Throw in your favorite motif/sts pattern. Keep on going until it is big enough to put on your head.
Some of my favorite items (knitted or crochetted) have been something I have made up as I go along.
I used some Cherry Hill Merino Lace doubled and crochetted a lovely scarf for a friend. I think I wouked a triple (or was it double) crochet stitch 3 times in every 3rd or 4th stitch, with simple SC base rows.
Hope that makes sense my almsot 2y/o is needing me and I gotta go.