I have mapped a fairly large area, Hull and most of East Yorkshire. When there was nothing on the map I just added what I found but now there is a fairly complete road network. Keeping that up to date can be hard work - how do you know what has been added since the last time I looked? OS Locator is really valuable for this as new roads appear on there as OS maps them. It would be better to know developments are starting and get in early and I think there may be a way: postcodes.
New postcodes are allocated all the time. Around a thousand are created every month in GB. The Office of National Statistics publish a postcode list based on Codepoint Open data but with some extra stuff in there. One thing is the month the postcode was set up. Looking at the recent ones may let us find places that need surveying.
I've created a map to visualise these: http://pcage.raggedred.net
I hope this proves useful.