buy wherever you get the right thickness. This is important, especially when you have a sunroof. If the material is too thick, you will have probs with the sunroof closing and also at the edges.
I have heard that the WLS headliner material is too thick. But check once more with them.
You MUST use 1/8 inch headliner material and NOT 1/4 inch. WLS sells 1/4 inch for E32. 1/4 inch material will not fit contours of roof grab handles, and other recessed areas of Headliner, and the sunroof panel will bind and stick with 1/4 inch material because there is not enough clearance. Most European cars use 1/8 inch.
But there must be other suppliers which can deliver this too.
Just did that some months ago. Pics are on my website.
You can even use fake snake or austrich
http://www.garysupholstery.com/ostrich.html