If you're using Lakeview, there's the Half-Moon Mill across the lake. Assuming you aren't a member of the Dark Brotherhood, Hert should be there to sell lumber. Though you have the moral quandary of buying wood from a vampire who feasts on travelers. Or you could hire a steward, which let's you buy stone, clay and lumber from him. Which brings us to our next point...It took me forever to find a mill that would sell me some wood. Went to Whiterun first but no one ever showed up with options for me to purchase, so I went to a different mill nearby and the only living thing for miles were chickens. FInally found someone on my third trip to a different mill and they will be getting all my business in the future since they were actually there to take my money.
ANY follower can be made a steward of one of the three new properties. Have whoever you want as a follower, go to the property, and select the dialogue option. They might even prompt the dialogue option themselves.How do you make someone steward of your house? Also, can I make Lydia my steward?
As an aside, they sheer amount of materials to build and furnish one the houses is insane. I'm to, like, 180 Iron ingots, 300 logs of sawn wood, 30 steel ingots, and a lot of damn stone. On the other hand since I've decided to make everything by hand instead of just having my steward purchase the furnishings, I've raised smithing by 21 levels.