General house thoughts and questions -

A tiny bit about me..
I'm a decently skilled builder with a low budget.  While 20k isn't NOTHING, its not even scratching the cost of a modern home.  20k likely doesn't even cover a permit, let alone everything else.
But I've done a lot of construction in the past and am probably adept as a builder.  But mostly with modern/ "to the code" homes.

My big question is how long would people expect a simple offgrid house with these key parts would end up costing in time?  If you ballparked hours of manual labor from start to finish, how many hours would you guess this below project would take upon starting?

Any and all your knowledge or info provided would be amazing!  I have searched - but suggestions help me fill in the places I've missed in my own search and discovery.

Key house points:
-Post and beam, in the style of old barns but wrapped in plywood/paneling and insulated for home living space.
-Low roof, low slope roof, live grass/flower roof.
-One level, cement/earth/cobblestone flooring, no basement. (House will be on the top of a hill, low drainage in the area or on this spot.  But likely I need to tamp down a hefty amount of gravel with some French drains just in case?)
-One doorway.
-Insulating walls after wrapped in plywood/paneling..  Wofati is interesting to continue a live roof with earth burmed walls for the insulative factor..  but I don't know a ton about it - would I still require insulation on the inside?

Luxury:
-Windows are a luxury that I'll invest in after the key points are finished.  
-Internal paneling after installing insulation is a luxury ascetics item.  
-Internal furniture.

Key questions if people have links or advice:
1. Anything and everything anyone can provide to me about living roof construction/materials/whatever.  I've bought the 50$ underground house from Mike O and everything else he has available and many other materials besides his.  Lots of discussions about Polyurethane or Pond liners for the sealing layers.  I can't think of something better then a pond liner though.. if its designed to hold tons of water from draining away, it could likely keep water off the roof too.  But I'd love anything else anyone can provide or give me insight on!  Please and thank you.
2. Flooring, as it'll likely be a mixture of cement and stonework.  While we're on the top of a hillside in the mountains I'm not too worried about water and drainage.  A healthy layer of tamped gravel then concrete.  But its never too early to ponder drainage ideas..  water is deceptively destructive if you don't respect drainage.  Would I want to also use pool liner below the gravel to reduce ground moisture from working its way up?
3. Internal insulation for walls/roof after wrapping and the space is enclosed.  After the live roof is installed properly, do I insulate it again from the inside?  From many videos and documents I've seen it does not look like I would.  But its worth an ask here!  As for the walls I know unless I did a wofati style with earth burmed on the outside walls I'd likely need insulation.. or both?  

Any answer to your question would have as many facets as a rubiks cube has faces.
Its impossible to answer in the form you request.
Search this site, there are topics which deal with building a single room and then over time adding rooms and changing the use of those rooms as the bui;lding progresses.
It may be the best way for you to achieve something.

Joshua Hozjan wrote:My big question is how long would people expect a simple offgrid house with these key parts would end up costing in time?  If you ballparked hours of manual labor from start to finish, how many hours would you guess this below project would take upon starting?

We spent $30,000 on just the interior of our house.

That was just enough to make the house liveable.  I doubt the interior will ever be finished in my lifetime.

I have an idea the interior of a wofati or earth berm would be similar though the exterior might be much more labor intensive.

I just received a quote for some pressure-treated lumber here in Puerto Rico, which might help you ball-park a cost where you are. A 4X8X(3/ sheet of plywood is $42 and a 12' 2X4 is $14.

I am in the process of building a log home.  It is 600 square feet with a 600 square foot loft and wrap around porches.  I can give you an idea of the hours I have into it.

I built all my tools out of scrap metal.  With a welder and grinder. The main tools being a sawmill. A tractor and winch, and a skidding arch.  Probably $1500 into scrap and maybe 200 hours of work to build it all.

Then I spent 2 winters and a summer of every spare minute of daylight in the woods logging and milling cabin logs, rafters and joists.  That was a few hundred dollars of fuel and maybe 1500 hours of work.

Once I was ready to build permits cost me $1300

I dug the foundation piers by hand in a drought, the ground was rock hard. $400 in material(cement an used electric poles) and 150-200 hours of labor.

The building of the cabin walls and roof went quick.  Maybe 250 hours.  I bought my screws second hand for $1000 and $400 for a cordless impact, skill saw and two batteries.

I spent this winter cutting lumber for my sub floors, finished floors and porch roofs. Maybe 400 hours and $100 in fuel.

I bought my insulation second hand for $1100.
I bought my windows second hand for $100.
The next biggest expense will be the tin roof.  Probably another $1500.
I am buying very little new.   If I cant get it from the woods I look for it second hand.  I am not installing plumbing, and very little wiring. It will have a small 5kw solar array.

I imagine I will have another couple thousand hours into it by the time it is finished.  

Not counting tools and permits I expect to have the basic house built for around $5000.  And probably 4000 hours of labor.

With better tools (like a bigger tractor and a bigger mill) those hours could be cut way down but tractors and mills cost money money to buy.

Cash outlay could be reduced if I used straw bales for insulation (baled by myself from my own fields).  And if I made my own wood shingles for the roof.  Code requires metal fasteners between rows of logs, I could have saved money by using metal nails only at corners and wooden pegs every where else.

For your roof as a cheaper option than pond liner, start calling commercial roofing companies and ask if they ever re-roof rubber roofs.  If so ask if they will sell you the used material.  Some times they will give it away for free.   Other times I have paid 10 or 15 cents per square foot.  That is what I am using as a temporary roof on my log cabin until I am ready to put the finished metal roof on.