If you follow the tutorial links which Zarai13 gave you to make the base hoop skirt and then attach hoops to the skirt. I started with 3 hoops attached to the skirt with one large hoop on the bottom, one meduim hoop in the middle and a small hoop near the top of the skirt. You can pretty much see where I placed the small and medium hoop in this progress shoot on the left ~ http://www.cosplay.com/photo/2706201/
One thing I warn you is that as your Rachel skirt progresses and more layers have been added, then you may need to adjust the hoops as you go along as they may not work with the weight of the skirt. I eventually had to put 6 hoops in total for more support and it worked well with the skirt and lasted for the enitre day at several events.
Something I will recommend is to make the hoop skirt and white underskirt ruffle with thin and light fabric (but not too thin to aviod the skirt being ripped when applying the hoops) The reason is because Rachel's skirt consists of many layers of fabric and the skirt WILL feel very heavy around your waist. I will also suggest making the black over skirt out of a thicker fabric which makes the hoop skirt unvisable.
Hope it helps and good luck with your cosplay.
London Flim and Comic Con 2011
Rachel Alucard from BlazBlue: Calamity Trigger
Riccotta Elmar from Dog Days
Nanoha Takamachi from Magical Record Lyrical Nanoha Force
Madoka Kaname from Puella Magi Madoka Magica