Best Book for Castle Building?

So I'm planning a no-stress 3.5 campaign for my group. We haven't played D&D for a while, but are looking forward to getting back to it after such a long break.

So the campaign is going to start off with NG's Crucible of Freya in which the PCs will end up with a ruined keep all to themselves. I'll be running various adventures using the keep as a home base and plan on the characters rebuilding and adding onto the keep...eventually to the point where farmers start to move into the area.

So I need a book that can handle both keep construction and maintenance of nearby resources. I have Fields of Blood, but its not quite right for this (but still an excellent book). WOTC's SBG doesn't seem to have quite what I need either. I've been reading reviews on Mongoose's Strongholds and Dynasties and it looks like it fits the bill.

Any suggestions?

"A Magical Medieval Society: Western Europe" is a very good resource for this. It involves some math, but it shouldn't be too difficult... and if I remember correctly, one of the examples include enlarging an older building.

I second the recommendation for "Magical Medieval Society."

I haven't seen Mongoose's Stonghold's and Dynasties but you can check out reviews of the book right here.