For that kind of money you are likely to pick up a real dog of a van and a total headache. Sorry to break it to you so bluntly.
Anything VW comes with "scene tax". I bought a tatty VW T5.1 van with 110k on it and paid £8k (minus my £2600 trade-in) to make into my camper. l I got carried away with the build and probably spent £20k in total, the Skyline Aurora pop top with solar and scenic canvas cost me £4.5k alone ! That said, I have a cracking van that I'm proud to own and will probably never sell. If I was building another I would contact a local mobile auto glass fitter about the windows as they can supply and fit for what it cost me to do the job myself.
For a £9k budget I would be looking to convert my own van, probably £7 for a solid base van and £2k to kit it out internally, enhancing the interior as your future budget allows whilst having the basics in place so you can camp in it. If you can do a bit of DIY all the info is online on Youtube, its a well trodden and well documented path. There are no shortage of suppliers of stretch carpet, insulation, lightweight ply, vehicle electrical items etc etc.
A pop-top roof is very expensive for not a lot of added feature, with hindsight I would buy a higher topped van you can stand up in, like a Mercedes Sprinter or a VW crafter for example. Be aware these can rust quite badly in places so don't buy the first you see. The only downside with a higher topped van is that some public car parks have height bars to stop the travelling community from setting up camp, which in turn prevents you from getting in. Its a small price to pay.