Should a hurricane safe room be part of my new home or home addition in Miami?

Yes. 

If you are building new exterior walls and concrete floor slabs as part of your project, the incremental cost of adding a few more walls to create a safe room is probably insignificant and could save your life!  

Wait, why do I need a safe room?

Because the truth is, no one is coming to save you.  

Many people have evacuated their homes only to have the hurricane chase them north, or have sheltered in place confident that the storm was headed elsewhere and then it zigged when it was supposed to zag.  That is the moment that your family walks calmly into the safe room and recognizes your genius for including a safe room in the design of your house.  If you do evacuate and return to a house with no roof, at least the important items that you locked in the safe room before you left are still there.  Again you are a genius.  

What is your plan when a hurricane comes? Where are you going when you evacuate? How long can you stay there? Are you better off there than you would be at home where you have friends, family, neighbors, supplies, tools, etc.  Your answer depends on what you have done to prepare. 

If you are in the enviable position of having the means to build a new house or an addition you clearly planned for your future and followed that plan with some rigor.  Chances are you are pretty well prepared for an emergency. Most people aren’t well prepared. When that large hurricane comes other people will need more help than you. 

How do you build a safe room in South Florida?

There are a number of ways but the most practical ways are all some version of a concrete box with steel reinforcing (rebar) and a heavy duty steel door.  

Nearly all homes in Miami are built using grout-filled concrete masonry units (GFCMU) so it makes sense to build your safe room with this common material.  The difference between the walls of the safe room and the exterior walls of your house is that each hollow cell of the masonry units will have rebar inside which connects the walls to the concrete slab floor/foundation and the concrete slab ceiling.  Each of the hollow cells will also be filled with concrete or grout.  This creates a heavy, solid box firmly anchored to the ground which can withstand large flying projectiles.  Even if the wooden roof of your house blows away, the concrete slab on top of your safe room isn’t going anywhere.

Another great way to build a safe room is using insulated concrete forms (ICF) which are kind of like styrofoam legos that are hollow in the center so you can add steel reinforcing and fill the center of the blocks with concrete.  ICF makes a lot of sense but hasn’t yet caught on in Miami. 

https://www.quadlock.com/images/insulated_concrete_forms/safe_room_construction_detail_sm425.jpg

Where should I put my safe room?  What should it include?

Most important is that your safe room is in an area that is safe from flooding.  If your entire property is in a flood zone, you can consider creating a safe room on an upper floor but the case may be less compelling. Safe rooms usually have no windows and have a steel door and door frame with multiple locking bolts.  Most rooms in your house have large windows which make them unsuitable as saferooms. A Pantry or utility room is often used because they have no windows and may already be where you store your emergency supplies. Bathrooms or laundry rooms are also good choices because your family could be locked in the safe room for many hours and a sink or toilet could drastically improve your situation (de verdad).  

How much does it cost?

I don’t know, but it will be pretty impractical to do on its own (rather than as part of another larger project), so if you want a safe room, include it in the design of your house or addition from the beginning.  It shouldn’t add too much to the cost of a large project and is easy to remove from the design if you decide it’s not practical in your situation.

Why don’t we just design my whole house to be like a beautiful, comfortable, energy efficient, safe room with a gorgeous tropical paradise surrounding it?

Now you are on the right track.  I like the way your genius mind thinks.