last updated 6 Dec 2022

Bottom Line:
Patios are cheaper to build but decks are a better investment.
The return on investment (average of numbers below) is 55% for patios and 80% for decks.

ROI:
Decks vs Patios | decks.com
Resources like Remodeling Magazine and HouseLogic show the ROI for a deck to be roughly 75% more than for a patio. As an example, a deck that costs $9,000 to build, maybe worth an additional $7,500, 83%, when you sell vs. a patio that may cost $3,500 to build and is only worth $1,500, 43%. when you sell.

However Is a Deck or Patio Better for Resale Value? | RST Brands says ROI's are:
Deck 76%; Patio 100%

6 High-ROI Outdoor Home Improvements | PunchListUSA
You can expect up to 69% ROI for your patio and 80% ROI on your new deck.
You can expect an ROI of 71% for an outdoor kitchen.

After the pandemic, more homeowners value functional outdoor spaces - like backyards, porches, decks and patios - because of the safety and distance they offer when people are sick.

How to Sell Buyers On Your Outdoor Oasis | HomeLight.com
A HomeLight survey of top agents estimated that a new patio costing $3,269 to construct would bring a $3,563 increase in value, or a 109% return on investment.


Deck vs Patio - other considerations:
Decks vs Patios | decks.com
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Considerations Deck Patio Pros & Cons
Cost $25 - $43 per square foot $5-$15 per square footPatios are cheaper to build, partially because the building materials are cheaper and because theyre installed flush with the ground, requiring less materials and labor to create stairs, install joists, railings, and other components associated with decks.
Lifespan Wood deck (10-20 years) Composite deck (25-30+ years) Patios can last for decades if theyre well-maintained. They do need to be cleaned frequently of leaves and other debris to keep them a clean, attractive place to enjoy time outdoors.

Composite decks, if well-maintained, can last just as long as a patio. Wooden decks are less weather-resistant than composite decks, giving them a shorter lifespan. However, regular washing, treating, and maintenance can extend the lifespan of a wooden deck.

Other considerations
e.g. flexibility
Easier to run services, electrical, gas, water. Easier to add heavy objects e.g. stove, fire pit, hot tub, fish pond.
See Deck Notes for materials

The cost of concrete ranges between $5 to around $8 per sq ft (0.09 sq m), including installation.

The value based on the above for a 400 square foot (20x20) space would be about $2,400 for a patio and $12,000 for a deck.

See Decks vs Patios | decks.com for other criteria.


Products:
Evaluating products is another project I haven't started yet.
Decks: Composite vs wood ; See Deck Notes
Patios: Concrete, pavers, brick, flagstone, tile, cut stone, loose materials (gravel mulch), ...
A Complete Guide to the Best Patio Materials | The Spruce is a good place to start.

Two eco-friendly products that sounded good are hard to find in the US.
Travertine Pavers Pros and Cons | Green Garage
Travertine is a form of limestone that civilizations have use in a variety of ways throughout human history. It is a useful product around pools, for garden walkways, and various other landscaping needs.

Travertine pavers do an excellent job of replicating the look of marble or granite, especially if you place them around a pool on your property. The price that youll pay for this building item is a fraction of what it would be for those materials.

If your intent is to build a patio or deck around a pool, then travertine is an excellent choice to consider. The porous nature of this natural material allows for additional water drainage when the pavers become wet.

The pavers that you find today that are made from travertine typically come from Europe and South America.

Timbercrete is an environmentally friendly construction material, produced from a mixture of sawdust and concrete. It reuses waste products and replaces some energy-intensive components of conventional concrete.
So far, timbercrete has been used to produce bricks, blocks, panels, and pavers, and can be pressed to create a great array of sizes, colors, shapes, and textures.
I could only find it in Australia as of December 2022.


Designs:
Google it you'll get millions.
500 examples at pinterest
Backyard Patio Ideas at Architectural Digest

Heat:
How hot do common landscape surfaces get in summer? | Ozbreed in Australia
temperature taken at 2 PM after a hot morning on a 104° day. temperature taken at 2 PM after a hot morning.
What °F
Air Temperature 104°
green grass 114°
shaded turf near concrete 117°
dry grass 125°
grass near gravel 126°
shaded concrete 122°
gravel in full sun 172°
grey concrete on a tennis court 173°
dark concrete drive 167°
light concrete paver 153°
dark clay paver 165°
Wet cast compressed limestone 143°
wet cast quartz 138°
Timbercrete† walls and pavers 121°
flat steel plate 159°
concrete surfaces around a house in full sun 167°
artificall grass 153°
Fine grade wood mulch full sun 147°
bare soil 154°
painted wood bench 154°
treated pine 144°
hardwood 163°
bitumen (semi-solid petroleum) 157°
plastic playground equipment 158°
metal play ground equipment
they were surprised by this.*
144°
vinyl seat on our outdoor vehicle 191°
* the metal equipment may have been cooler because the greater conductivity may have transferred the heat to the atmosphere faster.
Sorted by increasing temperature
Temperature taken at 2 PM after a hot morning
What °F
Air 104
green grass 114
shaded turf near concrete 117
Timbercrete walls and pavers 121
shaded concrete 122
dry grass 125
grass near gravel 126
wet cast quartz 138
Wet cast compressed limestone 143
treated pine 144
metal play ground equipment
they were surprised by this *
144
Fine grade wood mulch full sun 147
artificall grass 153
light concrete paver 153
painted wood bench 154
bare soil 154
bitumen (semi-solid petroleum) 157
plastic playground equipment 158
flat steel plate 159
hardwood 163
dark clay paver 165
dark concrete drive 167
concrete surfaces around a house in full sun 167
gravel in full sun 172
grey concrete on a tennis court 173
vinyl seat on our outdoor vehicle 191

† Timbercrete is an environmentally friendly construction material, produced from a mixture of sawdust and concrete. It reuses waste products and replaces some energy-intensive components of conventional concrete.
So far, timbercrete has been used to produce bricks, blocks, panels, and pavers, and can be pressed to create a great array of sizes, colors, shapes, and textures.
I could only find it in Australia as of December 2022.

Maximum time to hold your hand on a surface before it
 becomes too uncomfortable.
wet cast quartz 138° 	indefinite
light paver 150°        7 sec
Others 160° and higher	2 sec

Links:

Pros and Cons of Popular Deck and Patio Materials | New England Enterprises considers another option, Spoftscaping.
Softscape includes the living things (grass, plants, flowers, trees) in your landscape. Hardscape is the hard movable parts of your landscape. It include stones, gravel, paving, water features, decks, patios, and more.

Another option is a hybrid. Using artificial turfs which are very realistic now.
They have an advantage of being moe resilient when kids take a fall.

Artificial grass costs around $2 to $10 per square foot (0.09 sq m), excluding the prices of other essential materials, labor, and site preparation. The artificial grass turf aside, you need road base, weed barrier fabric, bender board, infill, and essentials like nails, stakes, seaming tape, and glue.


Examples with a combination of hardscaping (wood or cement) and softscaping (grass):

Links:
Deck Notes

Slabs Pavers and Flagstone | ParaSpaceInc

Artificial Grass vs. Concrete: Cost, Uses, Disadvantages | CaptainPatio



Pros and Cons of Popular Deck and Patio Materials | New England Enterprises