Earthbag roof

Hi, I'm planning a small earthbag house- round, about sixteen feet diameter and around two hundred square feet. I have a very limited budget, and found that both shingles and metal sheeting are too expensive for me to use. That leaves me with two questions- one, does anyone have any experience with living roofs and whether that would work for a structure like this? The book I am using shows a form of living roof with vigas and decking and above that heavy-duty pond liner, followed by bales of straw or hay which will naturally seed. That would work for me, but other sources on living roofs seem to have many more layers- a root barrier, a gravel layer, and so on. Question: do you think this will work, or that it will leave me regretting it when my ceiling leaks? I'm always suspicious of things that seem too simple! (The book is a very good one- Earthbag Building, by Kaki Hunter and Donald Kiffmeyer.)
Question Two: If I can't do the living roof and am forced to go with a dome (not my first choice) then will the cob and plaster I'd have to use to cover stand up to Southern Missouri weather? We have little to no snow, but the month of April brings rain AND rain AND rain. It seems that I'd be constantly climbing up patching it and things :) I've heard of lime possibly being something to use in that case?
Any help you can give would be much appreciated. I have under a thousand dollars but I've been tucking away for this for a while and refuse to give up now, although the cost of roofing kind of blew me. Thanks!

My suggestion, and you are more than willing to FTMAPMITJIYTIIS (Fly to Maine and punch me in the jaw if you think it is stupid) would be to build a cedar dome shelter. We recently has a discussion on them. I have never lived in one, and the photo I showed was just a toy to show my young daughters how to build one, but others have said they are very comfortable. I used to build them as a kid and stayed a few times overnight in them in the dead of winter and found them warm...and I live in Maine! In that case the other guys just used branches to form a dome, or in lean too shelter like mine, draped it with plastic, and then lived in that.

As you live in there, rain free, you could build your walls up in earth bag fashion, making the structure refined as time marches on. I could easily see that being done for $1000 in materials even if you blew some of your budget on a great woodstove (used).

Try doing a photo search on Primative Shelters for ideas.

Where I live, 100 years ago Colliers and Surveyors for the logging companies used to build bark lined cedar domes to survive.

There is no reason why you could not make your own shingles either. Today they are standard in size, but the old "shakes" used to be 24 inches long, but they could be 36 inches if need be. It would be a pain to hand cut wood rounds for the shingles, but a chainsaw would make light work of it, and then a homemade froe and cheap used drawknife would get you there. As long as they were buried under several inches of soil, they would not rot because there is no oxygen getting to them.

Bark taken from trees in sheets would also work. We always used Hemlock here, but I think cottonwood comes off in sheets too and is thick like eastern Hemlock.

I'd rather not punch you in the jaw, because you might punch me back and then I'd be in trouble :) but I am living in a house with family at the moment and building my little house on the same land. So I'm not in need of shelter. Also, the trees here are mostly very young due to forest management, and finding even large ones for beams is a bit of a challenge. I haven't done much like this before (although I've built things with wood and know my way around most tools) so I doubt I'd be able to make my own shingles as easily as you :) I'm trying to get it done before spring (April-March) because of garden work after that; is that too unrealistic with me and two or three helpers?

I think the beam-decking-pond liner-bales roof is a good idea.
The hay n' straw compost could protect the liner from UV rays, I would add somethimg to hold the compost in place, like orchard netting or chicken wire.

Any roof should extend  past the walls to protect the wall finish from rain.

One board member  used scrap lumber, plastic from matress packaging,concrete and used carpet to create a sturdy living roof.

[i]If I can't do the living roof and am forced to go with a dome (not my first choice) then will the cob and plaster I'd have to use to cover stand up to Southern Missouri weather? We have little to no snow, but the month of April brings rain AND rain AND rain. It seems that I'd be constantly climbing up patching it and things :) I've heard of lime possibly being something to use in that case?[/i]
Consider KEIM mineral paint instead of lime. See https://www.youtube.com/watch?v=q7cKpJ8ymOA&t=125s and you will be impressed.

I am hoping you have a bit of income to supplement your budget as time goes by--there are bound to be some unpredictable costs along the way and it would be unfortunate to stall the project. Another option might be thatched roofing--I don't know if you have invasive cane along your rivers like we do in south Texas, but I have pondered using bundles of that. But as long as you are willing to experiment and live with possible failures I would say go for the green roof idea!

you could do a yurt style ceiling with all of your rafters reaching to a center post. I would recommend this method over doing a reciprocal roof, which would be amazing, but difficult if you are building alone and no experience with such methods. After rafters, do an inexpensive sheathing like salvaged wood--pallet or other reclaimed stuff--if you don't want it to show get some burlap or other cloth for the ceiling. Get free water proof membranes like used billboards from advertising companies. Then pile on the straw, hay, organic material for a living roof. Some layers of cardboard on the liners will help prevent them from being damaged. If you can get some insulation under the tarps/liners then you are really set.