Non-standard build homes in Puerto Rico

If my wife and I decide to spend more time in Puerto Rico, maybe 4 months per year, my ideal setup would be:

1. Bunker like home, underground or built in side of a cliff.  Probably higher elevation, depending on ability to flood-proof a bunker.

2. Home itself would be used as storage for a small car and small amount of personal property while away.

3. Above ground would be just some simple structures for shade and relaxing, a BBQ, hammock, table with some benches, and parking for while we are there (2 months at a time, twice a year).

I would like to do 100% of construction myself, my wife and I, we have built two very nice homes -- one in the city, tore an existing 2000 sq/ft home down to studs and rebuilt it, and another 2000 sq/ft home in the forest starting from bare land (no power, no water, no sewer, no foundation).  This home would mostly all be masonry/concrete.  I would need to rent or buy (and then resell) an excavator for digging and bring in concrete trunks.

How strict is Puerto Rico on building permits/processes?  Where I live now, these things don't exist (or nobody cares), so my build would look something like this -- how far from Puerto Rico would this be?

A. Buy land - close in less than 30 days, pay cash, pretty simple paperwork with real estate agent helping.

B. Rent excavator - $200 delivery and maybe $300/day for equipment that could dig a 12' deep hole fairly easy - no problems operating myself (no licenses/registrations required to rent)

C. Forms/rebar/etc for concrete prep - easily available from local Home Depot

D. Concrete delivery - just call a few days ahead to have delivery, between $100 to $150 per yard delivered, 5 to 10 yard minimum, pumpers available for extra fee per yard -- hourly fee applies if truck spends more than about 15 minutes per load.

E. Steel door - long drive to steel yard, high prices, but availability is good for basic stuff like 1/8" to 1/2" plate, angle iron, box, channel, and other common items.

F. Lumber for misc needs - local Home Depot

I've driven by Home Depot in Puerto Rico (I think so), and it seemed like Home Depots I have been to in USA and Mexico, pretty standard, so I think the basic home building stuff would be available easy enough, especially for someone not in a super hurry.  Not sure how prices compare to USA, in Mexico prices are double the USA and tools/products are inferior (i.e.-you can't even order Makita, Black and Decker has special model numbers for Mexico only, etc).  Not too worried about brand names though, if it lasts to finish the job, I'll throw it away (or give it away) when done, good enough.

In the USA I think building an underground concrete bunker about 20x20, 8 to 10' tall, would cost me around $30,000, if I did all of the work myself.  This would not include tools I need to buy, or the price of the land, or fees to any utility companies for running power, water and sewer.

Reasons for this maybe bizarre idea: I like being able to come/go as I please, not needing to make reservations or depend on others (hotels, AirBnb, etc).  I like being able to leave some personal items there, make travel easier.  Having my own car, and not have to rent.  Ability to leave my stuff and not worry (too much) about theft or natural disasters, like I would have to worry about with a traditional vacant home.  Yes, a bunker could flood, hence the cliff side or high elevation ideas.  I enjoy building stuff, and even if I only stayed here 1 or 2 times, I wouldn't care, as long as the building process was a fun experience for my wife and I, and we didn't sink our entire life savings in to it.  $30,000 spread over a year long project isn't a lot of money for us.  Buying the land will probably be the hardest step, a lot of cash (or debt) quickly.

If we buy land without power, water, or sewer, how hard are those things to get?  Does your house have to be permitted to get those things?

Edit: we are fluent in Spanish and English, so assume language will not be a problem

- @shopguy