What a fun project! It's a big question and I can't give you all the choices in this answer but let me suggest a few things.
First, I'm assuming the house you are designing is in Tampa, because that is where your letter is from. This means you are designing for a humid, subtropical climate.
I suggest your start by orienting your building along the East West axis so your do not have windows facing the last, long hot rays of the Western sun. I also suggest you orient your openings to capture the prevailing breeze.
Use massive materials
For materials, you might like to take advantage of a heavy mass material like concrete block, insulating the outside of it so that you can keep the inside cool.
Massive materials, like concrete block, capture hot or cold and release it later, kind of a delayed reaction. But it will release it in both directions (inside and out) unless you insulate the outside. If you have cool nights and hot days, you open the house up at night and close it down during the day. This is rather simplified, but the point I'm trying to make is to choose a material that can work for you so you don't need as much heating and air conditioning.
Sometimes the specific climate and location warrants the exact opposite material, a very light weight one like wood, so that there is no heat build up at all.
If you are using wood, you can specify engineered wood, made of small pieces laminated together, so that post industrial reclaimed material can be used in making it, or wood certified by the Forestry Stewardship Council, which certifies a forest has been managed in a responsible way.
- You can also specify "Advanced Framing Techniques," which use less wood than standard framing.
- It is sometimes difficult to use reclaimed wood for structure, if its strength hasn't been recertified. It is important if you do use reclaimed wood to verify it doesn't have any termites and wood boring beetles in it.
- All solid wood structure is recyclable if it is in good shape, meaning all solid wood can be used again, if not for structure, then for interior cabinetry and trim.
If you are using concrete, you can specify a recycled product. like fly-ash (a by-product of coal production) to be part of the mix, and actually makes the concrete stronger.
Of course, your foundation will be concrete regardless of what your walls are.
For a roofing material, you will want to specify a "Cool Roof" material, one that reflects the hot rays of the sun, rather than absorbs them. Or you could design a "Living Roof" or "Living Wall" and let vegetation cool your roof through the release of moisture while creating a habitat for all the little creatures displaced by your new home.
After your structure is designed, you can have some fun with the many choices of finish materials using recycled products, such as glass and ceramic tile, quartz stone counters, and compressed paper counters.
Have fun with this. There are many options and many techniques out there and you can invent some of your own.
It is my hope that the students of today will find many more ways we can design eco-friendly homes that are fun, beautiful and affordable.
Here are some websites you might want to visit
Advanced Wall Framing
Eco recycled surfaces
Building Science Corporation (anything on their website about "Hot Humid Climate" would apply to your area)
Fly Ash Concrete - Build It Green
Green Roofs for Healthy Cities