I do have a pretty sturdy reserve fund tucked away for the rental house I already have, probably enough reserves for two SFRs actually.

In order to get to it I have to start off small and lay out a sturdy foundation.

I am going to continue to dive deep into this, and I know with enough knowledge I'll be able to build a sturdy foundation.

Although it would cost more, it would look nicer than the metal shed you're considering, and would be more sturdy and functional.

To manage the risks, your lease should be on a short leash, but renewable.

Use of sturdy materials (although not necessarily the most aesthetic) generally works better than spending on lower quality materials which look nicer.

Primo is right in that you need to have some put aside before you cut the leash.

If they want to add a unit (or 10 units) they should purchase where the current zoning allows the addition.I fear these low density rural areas that want to maintain properties that allow horses, goats, off leash dogs, etc. will eventually vanish (at least in the suburbs of highly sought areas like coastal CA). 

@Brian Spies I agree 100% that cash is king and that none of these approaches make sense without a long leash of cash reserves.

Make sure you keep the PM on a very tight leash.