the hood cover illustrated in photo by CA with all those clips at the back wasn't actually OEM for the S4 [Edit:....that's why they write "Hoodbag to suit Series 4 spiders..." (although I am sure it would fit, it is not strictly correct and these with all the clips showing just do not look as nice when fitted..imo)
the S4 original cover is this type, it has a zip up part that drapes behind the seats (sort of storeage area if you will!) OKP Parts and Engineering GmbH
then you need to buy 2 of the hard wings, that are glued to the cover so you can fit it to the car! (so you need to buy the correct glue....these really need stretching to fit, so the glue has to hold darn well, or the fit will just look amateurish!!) OKP Parts and Engineering GmbH
so all in all you are looking at at fair bit of money.
Your best bet would be to pick one up s/h from fleabay