We have one off the side of the house, it's about 18 feet wide by 25 feet. At our old house we had a 4 foot by 25 foot space that was the dog run, which was mainly used for 'go out and potty'.
Ideally you want something that is off the house so you'll be able to let them in/out without treking to the run, and something that isn't going to block the rest of the yard from being used. We put in a dog door and it's great, other than they track in and out and Storee likes to take things out to destroy. So we have a locking one now. I like a natural surface so we've been using straw, it's cheap and while it does track a bit, it stays clean enough and we can replace it fairly often. I didn't like cement because it looked gross all the time, unless we sprayed it with a pressure washer or bleached it (smelled too). Shade is another consideration but you can always put up tarps or build something as needed for extra shade.
Even if it's small, it's better than them destroying the yard and if they get out for walks/runs anyway...
I'd be interested in seeing pictures if possible? Your setup sounds great, but I'm visual...We just built one that is 12' wide by 45' long along one side of the fence. We put a 4' chain link fence to close it in and stairs directly to it off the deck with a gate closing off the rest of the yard at the top of a second set of stairs from the deck to the yard. We framed in a wood border on the ground and used washed rock, a type of round smooth rock about the size of a nickel over top of landscape cloth to block out weeds. You can hose it down. Our dogs go out there to potty only and don't stay in the run. They go back up the stairs to the deck and inside the house after.
I am still working on an escape free enclosure for Dakota who thinks her middle name is Houdini. Her sister opens her crate door with her tongue, but won't leave it without permission. Last night she ran ahead of my son and opened the yard gate for him and then sat down. She stayed in the yard. But Dakota? No, she has to find every possible puddle to roll in and then see if her sister is out. She doesn't leave my full property (My house and yards are at one end of my property, about one-fourth of it). But I hate to have to leave her in a crate when I go to school (teaching) on a beautiful day. She will dig under the fence if I put her in a yard with the gates chained. I never thought of a wooden floor for a run. Great idea! While I have people here most of the time, it is in and out.I have always used dog runs, to give the dogs a safe place to be while I am at work during the day. I have also learned a lot over the years, as I have had some very destructive and smart Goldens!
My runs are smaller, 4x16. I like them longer than they are wide, so the dogs don't get in the bad habit of circling constantly. They are Mason kennels and honestly are the only ones I have found that will keep in even my worst escape artists. With a Mason kennel, the chain link is securely fastened to the top and bottom rails every place it touches. This prevents the dogs from pulling up the chain link and escaping, or even worse, attempting to escape and getting stuck. They are 6 feet high, which so far has thwarted even my climbers, who tend to get about 4 feet up and then just hang there enjoying the scenery The gates are impossible for a dog to open, and a lot of people haven't been able to figure them out either! I have had several who were able to open regular fence and kennel gates unless they were padlocked.
My runs have a wooden floor, which is not ideal but was all I could afford 10 years ago, and so far, so good. I use ginseng cloth in the summer as a shade topper, and it works really well. They have some very heavy, well made dog houses for shelter if needed.
When I first moved to this house, I attempted to use the (very nice) sheltered kennel that the previous owner had used for their 2 labs. I put Rikki in the run and by the time I got to the house, she was waiting for me on the steps! It took her no time at all to peel up the chain link and slip through it. My other girls, Kahli and Scarlet, were fully capable of opening the kennel and yard gates at their handlers house and letting themselves and the other dogs out as well. Escape proof is very important to me!
I prefer having the dogs out there, with all their outside toys and plenty of water, as opposed to being in crates or even loose in the house all day. Living out in the country, there are plenty of rabbits and birds for them to watch and lots of toys to play with. When I come home, they get some play time in the exercise yard and then come in for the evening and night.