Any flat white wall does an excellent job in a "perfect" dark room.
Anyway, it's a good and cheap start point to see what you projector can do and check what it is its worse weakness: black rendition.
If you want a "true" screen and you're happy with the blacks on the white wall, get a screen based on the Da-Lite Da-Mat fabric.
If you're not happy with blacks, get Stewart Grayhawk fabric.
To appreciate my judgment, you should know I own the VPL-VW10HT and the Grayhawk, but never saw the Da-Mat. I did some paintings test which never obtained good results with ambient light, not your case. On dark room, differences between white wall and Grayhawk is not obvious, except that on Grayhawk the picture is globally dimmed (thus helping the black issue).