If you look at the classic, historic English farmhouse, you will usually find that it was built over several generations, a room or two at a time. Sometimes a wealthy generation might add an entire wing.
So I might look at building in stages.
I'd start by using some of your timber, or whatever local lumber you prefer, to make a 'pole-barn' roof. Give yourselves a big
shelter to work under. You can build right up to this and let it become the roof of the building, if you like. Leave wide eaves on all sides of the walls (3 or 4 feet for a walkway if possible).
Do some research to learn about drainage and footings. You want a naturally well-drained site, and slopes or perimeter drains to daylight (someplace naturally downhill of the drain trench). I might grade the entire area to a well-drained level, but build each set of foundations as I needed them rather than staking out the entire future building at once.
Plan out the first room at one end as the 'practice shed,' which can attach to the next room(s) if you like how it turns out.
If you get discouraged or find a better method, the stone 'shed' can always become the
root cellar for a different type of house. So I might build it on the north, east, or shady side of the future-house
footprint.
I like the idea of a 3' or 4' tall rock wall, you can keep going up with rock if your skill and supplies allow. Practice a couple of times to figure out whether you can build vertical, or whether you need a wide base so your wall can taper a bit (depends on your skill, mortar, and shapes of rocks / ability to cut and dress them).
Once you collect all those rocks you very well may find some sticky clay-like soil underneath some of them, or get a good local source for "ready-mix" clay/sand soils.
The mineral soil you want does not need to be all clay. We have found "sand" on some places with enough clay in it to make great cob. What you want is an area that gets rock-hard if compacted, and doesn't dust off or crumble once it dries out.
It is entirely possible for two little ladies to build a house that suits them. But it's definitely a fair amount of work.
Whether this will be a 'modern' large home, or a more traditional country cottage, depends on your time and resources.
If you have the social capital to recruit a bunch of help, a few 'barn-raising' sessions could be a big
boost.
If you don't want to hand-dig the drainage, or raise the roof without help, you might look into swaps with local tradesmen. Don't be afraid to use lady-like skills like baking killer pies.
Do be aware that help tends to do things their way, and it's hard to make them fix it even if you're paying them. So choose areas for this kind of community boost where you are really stuck without it, and/or you can tolerate the quality of help you get.
Taking a cob workshop, or helping on someone else's
project, is a very good idea to get a sense of how it's done, and how much work you are committing to with a given size of building.
If possible, get some hands-on practice repairing someone else's mistakes, it's one of the best ways to learn.
Here's an English website about repairing and proper detailing for traditional buildings:
Mike Wye & Co
Here are a couple of other English sources:
http://www.buildingconservation.com/articles/earth/earth_buildings.htm,
http://www.buildingconservation.com/articles/wattleanddaub/wattleanddaub.htm
It's also worth noting that a cob house is not likely to be the most affordable building in this day and age.
Many of the historic cob structures that survive are examples of excellent architecture, not cheap "mud huts," and would have been very expensive in their day. In modern times, the cheap fuels for shipping manufactured materials make it even harder for cob and earthen building methods to compete.
Earth Block building article.
The only context in which an earthen building is 'cheaper' is if you are committed to using no carbon-emitting processes for your project, you have materials locally available, and you provide all of the labor without counting the cost of those labor hours and resources toward your project. e.g. if you hire workmen for pie, and don't count the cost of the pie.
Otherwise, the costs can be 10% to 25% more than with conventional, contemporary housing (such as wood-frame or manufactured homes).
Building with cob, like building with stone or masonry, is an investment for the ages. Rare nowadays. Sounds like your
roots are deep enough in your local soil that you might just pull it off.
You might see if your 9-year-old son is excited about some aspect of this 'castle', and get him involved at least to the extent that he can build his own room (or detached cabin) when he comes of age.
Yours,
Erica W