I would suggest that you need to get your Hibiscus planted in the ground or a container and allow it to establish itself before you even consider trying to take cuttings from.

It does depend how large the plant is - the height and spread at maturity of this one isn't huge, however, making between 5 and 8 feet in height and about 2-3 feet in width. If you can find any shoots suitable for cutting,then have a go, but if you don't have a heated greenhouse, its probably better to wait till next May or June. You need shoots about as thick as a pencil.

Alternatively, you can grow from seed collected from the flowers - instructions for that (and cuttings) here, you'll need to copy and paste in your browser

http://homeguides.sfgate.com/propagate-hibiscus-moscheutos-25648.html