I make this a few times each spring with my daughter, it's a fun thing to do and it tastes pretty good too.
We tend to use 200 Dandelion heads (you can just use the petals for a slightly cleaner taste) with 700ml of water and 700g of sugar - This makes 2 standard jars of honey
Pro tips: Pick the dandelions at midday/full sunlight and don't wash them as you want all the pollen. Just give them a shake and leave then out in the sun for 30 mins to allow anything living to crawl away.
Also when reducing the syrup, to test consistency, put some on a spoon and allow it to cool on the side for a couple of mins.
It's easy to over reduce and the syrup will be runnier that you would think when it's actually ready (it obviously thickens up as it cools down).
Macca