Cob, straw bale or earthbag for hot humid climate?

I've read pros and cons for each but would like some personal opinions if you guys don't mind.

We live in Alabama with temps averaging about 90 during the summer (with lows around 70s to 80s) and temps around 35 a month or two out of the year when it's winter time. Humidity here can be well into 90% on average. And annual rainfall is about 53-57" a year.

We do NOT need a permit where we live. I will be building it myself about 50% of the time with one additional helper a few days a week.
I can spend a solid 8-10 hrs each day building and on the days when I have my helper, it will be the same 8-10 hrs a day for each of us.
Timeline to have it built is 2-3 months.

The house will be no more than 500 sq ft with a fence wall built around it to keep out local wildlife so our future garden will be protected. The site already has power and water that we can tie into the new build. We also have access to free pallets to build furniture and things of that nature. If straw bale is the best option, can we use pallets to build the post and beam frame/roof and use bales as infill?
An earthen floor is also what we're leaning towards throughout the house with the exception of the kitchen and bathroom where we would use a brick/tile on sand method.

Given our needs and our climate, what type of home would you suggest? I have not done a soil test yet to determine if ours would work but if it doesn't, we're leaning towards reject sand for any fill needs.

We have also considered one of those pre-built wood storage buildings and finishing it ourselves to create a liveable space. Thoughts?

If you need more info that I haven't thought to provide, ask away. Thanks in advance!!

I think any of those would work for you, as long as you have a good hat and boots (wide roof eaves to keep water off the walls, and a stone foundation to keep damp from rising.) Depending on the humidity, you might have issues with cob growing mold before it dries. In any case, I would build the roof frame first so the walls can be protected during construction.

Pallets are a good resource, but not for structural posts and beams, unless you have the knowledge to build laminated timbers from them. It would be much cheaper and easier to buy some lumber, or cut some modest-sized trees, depending on your resources.

I live in a similar climate, though slightly more dry being in central Texas (may move to northeast TX).
I've really liked cob.  For a little while I looked at rammed earth and earth bag building, and they have their pluses.  After that, light straw clay looked best.  I still think light straw clay is best if airconditioning will be used in the southern US.  I'm still drawn to cob though, even for a small rectangular home.

Do you plan to make the wall load bearing, or make a wooden structure to hold up the roof?  I've read that only experienced cobbers should build a cob home where the thick walls hold the roof.  My experience with cob was just a couple of hours in a permaculture design course.

My experience with construction in general is a little beyond that, but not tremendous.   I've been a carpenter's helper and a pipe fitter, then I built a 180 sq. ft. tiny barn apartment that I'm still working on, part time, 1.5 yrs after starting.  I'm just on paint and trim now, but I hate conventional wall coverings, flooring, and trim.  I  enjoyed the framing though.

The next home I build will be stick frame, but the studs will be 24" on center, and there will be a single top plate since the rafters will connect to the top plate right above each stud.  This meets building code (if that matters for anyone else) and is called optimum value framing.

I'd consider cobbing around that type of framing.  The ceiling joist would then be 24" on center too and that's great for attaching the ceiling material of choice.

A thick earthen, cement, tile, or stone floor should help cool your home.  Place a window high up on the wall to exhaust heat.  Find out where the summer breeze flows from.  Place water tanks or ponds on that side of your structure.   Plant lots of plants.  Shade the home with vines on trellises if the trees grow slow, or there's no room for trees.  Use porches or big overhangs and consider a dog trot floor plan, so the wind will speed slightly between the two little portions of the house connected by the roof.  

Yes, I do believe people can build without taking these courses.  Don't be afraid to make mistakes and build a smaller less important cob item first, maybe a fence portion.  

There is a ton of info / images of 2x4 framing online, and many people you know will know at least a little bit.  
Of course, hunt for used wood, but 2x4's are worth it.

An alternative to stick framing would be pole barn type framing, but ceiling joists would be separate from the fewer rafters, then perlins would connect each rafter beneath the sheating.   I don't know if pole barn construction would save $ or materials, unless you have/ can find sizable round posts.

Timber frame is more costly, especially when paying retail for the timbers.

Still, strongly consider framing this earthen structure.

Edit:  I realized after writing that you are probably very attracted to the round organic shaped home.  Building without a wood frame would definitely save you money and fits that wall shape.   Do you have time to practice cobbing?  Maybe you can learn on your own to build well enough to make it load baring.  I don't think you're in an earthquake zone.  Also, putting a light roof (not soil )  should lessen the load that the walls will carry.

As someone else in the hot and humid south (lower Alabama actually) this is something I've looked into. Earthbag would be great...if it weren't for the fact it is no longer anything like affordable as it was when the major Earthbag books were written. I would strongly advice against straw bale, my understanding about cob's molding issues is that it primarily comes from the straw mixed in and the high humidity here almost garuntees heavy molding in strawbale construction. Moldering strawbale are going to rot away and cause some unpleasant health issues in the process...unless someone out there knows how to keep this from happening in which case I'm all ears.

Cordwood construction looked promising but due to construction delays we've lost most of our building supplies...they will make some healthy garden soil but little else.  I wish you the best of luck.

A quick search of the interwebs yielded quite a few strawbale homes in Alabama in various areas...there's a community down there called Common Ground, you might try to look them up for a visit.
We were worried about the humidity and crazy weather changes we have here in KY in regards to strawbale construction...visited a few homes and every one of the owner-builders said that mixing lime into the straw/sand/clay/water plaster mixture is a necessity for the exterior, plus having excellent drainage and a good stem wall design. One said he touches up his exterior every 3-5 years to keep it solid, another said they retouched the lime plaster mix after a particularly wet winter. Their homes were gorgeous and well-built.

I know you mentioned humidity as a possible issue, I am in coastal Georgia, has anyone had any issues with pests breaking down the cob structures?