Some thing like that Aspects but the most important part is the fall arrest bit.
Can I suggest you call in to your nearest safety shop, someone like safety direct and ask them loads of questions and get to see the rig before you buy it. They range in price over here from about €80. 00
The safety wire you connect to on the roof should also have been certified at least annually, you should be able to find the cert record somewhere on the wire. Don't use it if you are not happy it has been tested.
Hope this helps