I would angle them down and keep them horizontal to enable stereo sound like this:

Ah ok great thank you! Someone said this to me but is that completely wrong?

“Vertical should be best if you have two paired. Horizontal is best if you only have one speaker.”

The room is quite high so I am guessing they would be perhaps 3 metres up in the air.

From the Sonos Five User Guide:

“For a single Five speaker we recommend positioning the speaker horizontally to enable stereo sound.”

Even though you have three Fives, they are positioned so far apart in the room that they are each acting as individual speakers. So go with the horizontal position so they play in stereo.

Read more here:

https://www.sonos.com/support/en-us/sonos-user-guide/index.html#t=sonos-user-guide%2Ffive%2Ffive.htm

Ah ok thank you that helps alot.

In your opinion, and seeing the images would the 5’s be the best speaker for our sound and space?

It depends on what you are trying to achieve. What is your business? What type of music are you going to play? Do you want it to be loud or is it just for ambience?

It will be a gym… the music will be part of the classes as far as background noise, but if it was a hard workout we’d turn the music up to be loud.

They would be the best Sonos speaker.

An alternative that would get you a lot more sound would be three Sonos Amps and stand-alone speakers. Look for high efficiency and decent sized woofers to fill that big space.

I feel like three Fives mounted on the side walls may not be enough. I would consider doing 5-6 speakers - 3 speakers mounted on the front wall and 2-3 speakers mounted on the back wall.

Another option is 6-8 pendant speakers hanging from the ceiling and powering them with Sonos Amps. Or do a combination of both the Fives and pendant speakers.

For a setup like this, it might be best to contact a professional audio company so they can come out and make the best recommendations for your space.

Based on what I observe in gyms, people seem to enjoy thumping bass during workouts. If this is your preference, I recommend a subwoofer or two. And I agree with Stanley_4 that passive speakers and AMP(s) would be a good choice. Unlike a Living Room stereo system, you are attempting to create a certain ambience, not a simulated concert hall experience. I also recommend using more than three speakers.

Three Amps set to mono would give you six speakers and outputs for three subs with independent or grouped volume controls for each Amp. 

Many years ago I worked for a pro audio dealer that sold Cerwin Vega gear. It was beyond amazing.

A few of these with a single Sonos Port sending them music might not kill your budget.

https://cerwinvega.com/cve-10.html

Some of the bigger stuff would but you can dream.

https://cerwinvega.com/pro/powered-speakers.html

Thanks all, this is beyond helpful!!!