OK, where to start...
I think I'll just go 'row by row' with replies...
>starting with around 10-12 birds
Question 1: are you starting with eggs or keets?
Either way, figure on about 10-20 % loss in the first month or so of free-ranging because they are the stupidest thing God ever put a feather on. Our neighbor started with 47, by the end of the 3rd month, she was down to 24, and she now has 8 that have survived past the 1 year mark. All of our girls are eggs from her hens that we rescued because they were laid then abandoned. We kept finding clutches of eggs (or eaten clutches) that the idiots had forgotten they laid or had laid, just went walkabout, and never bothered to return to. Long story short: if you want 10 - 12, start with 20 -30.
>The floor is black top with concrete curb
Much like chickens, guinea foul scratch & peck - it's instinct. While a bit of grit and gravel are good for them (along with oyster shell) blacktop is toxic and I hate to think of what that would do to their system, to their eggs (are you planning eating their eggs?) and especially to their offspring. They need dirt to scratch in, to bathe in... so I have serious reservations about the blacktop.
>the roof would be about 6’ high with pitch
IMHO, the roof height is more about your comfort (walking under it to clean...) than theirs. We have an offset layer of chicken wire (to keep predators out) over part of the run, and galvanized steel (that rippled stuff over patios...) over part of it for shelter from rain/snow/hail (because, again, they are too stupid to come in out of it.)
A couple of other things that come to mind:
Smell - - guinea produce a smell that is like no other (and I nose-blind to a wealth of odors) so I would question whether or not you really want that 'aroma' so close to a door that opens directly into the house.
Insects - - The above mentioned smell seems to be a natural survival mechanism for these loonies in that it attracts a wealth of insects (all you can eat free buffet!) It cuts down on the feed bill, but do you want the insect population that close to the house?
Heat - - If you are starting with adult birds, heat is not much of an issue, just give them time to acclimate if you're bringing them in from one clime to another. For youngsters, the vet clinic sounds like an optimal spot for hatching/brooding because it's enclosed, has electricity, and in close enough for daily check-ins. For some reason, consistent temperature seems to be more critical for hatching eggs/keets than it does for chickens. They are all sensitive snowflakes I guess...
Acclimation - - From what we've found, acclimation is key, whether it's temperature or location. For keets (& youngsters) **slowly** lower the temp of their environment to match where they will be living outside. For newly hatched keets, you want to start @ 95-99 degrees F, reducing by 5 degrees F each week. Environmentally, if you don't want total strangers showing up pounding on your front door asking, "Are those your turkeys running down the road?" you will want to start with them living in an enclosed run and then get "play dates" (ask your wife, she'll explain) with the great outdoors. Once they are accustomed to the wide wide world of sports and predators and cars and dogs, you have a go at leaving the run open for them to sprint into like scared mice when the wind shifts, the horse neighs, or the neighbor's dog breaks wind. Of course, when an eagle swoops over screeching menacingly, they will stare up at the sun screaming, "Big yellow orb!" as they're scooped up and carried off. Did I mention they're idiots? Keeping their familiar food & water containers in the run will remind them that, "Oh. Yeh. DUH! This is where I come back to." OK, honestly there's a 20-30% chance that they'll remember to come home, and maybe a 10-15% chance they'll move when a semi is barreling down on them at 65 MPH. But the food serves as a reasonably good reminder as to where they 'live.' And when you find their lovely spotted feather strewn across the yard? Well, at least you'll know you've done your best to give them what they needed to survive; 'case we guinea folk all know - nature sure as hell didn't.
Socialization - - Our girls are hand raised (the advantage of having kids in the house) so they know us. They see us coming and run to greet us. This provides a measure of assurance that they know where home is, we can keep a head count, and we can 'casually' follow them through the yard to a thicket or bramble to see where their nest is and keep an eye on it. Unlike dogs, microchipping isn't a really viable option for keeping tabs on them (doesn't work for squat on wives either) so knowing them and them knowing you has countless benefits. Because, do you hear what's coming? Because in spite of being dumber than dirt, they are incredibly social creatures and they will imprint on you and that provides a measure of safety for them and peace of mind for you. The downside, of course, being that if one of them becomes fox food - it rips a chunk of your heart out (and you're stuck telling yourself, "I told you not to get so attached to these idiots!")
All this being said, they are lovely graceful creatures, comically useful alarms, watch dogs who rid the area of unwanted pests (tics & snakes are just the beginning, crabby neighbors will stop dropping in to complain) and they return the "feed me" favor with a plethora of delicious *bigger* eggs.