You *can* keep meaties and layers under the same roof, but if you have the option of NOT doing it, that'd be better. Reason: meaties, as normally kept, create QUITE an enormous amount of moisture and ammonia, which is hard enough to control on their own behalf let alone wanting your layers to be affected by it. The ideal situation in most cases would be a very open coop for the meaties, e.g. a 2- or 3-sided shed, with mesh on the other sides and the ability to put a heat lamp or heated hover in the back-most corner of it for when the chicks are young (in conjunction with an additional windbreak or draft-guard for that period)... and to have this be either a totally separate building from your layers, or to have it as a lean-to extension off your layer coop that does not share any ventilation with the layer coop.
As for a run, if these are typical CornishX meat chicks you are wanting to raise, it is really better to give them their own run. (A lot of people do not give them a run at all, but I think they are much better off with it... more exercise, healthier, more muscles, lower death rate, happier birds). First, because they will make the same horrible crappy stinking wet mess of the run as they do in the coop; but also because, after the first few weeks, they tend to become extremely couch-potato-y and fair game for pecking by more active chickens. Also it will be easier to ensure that everyone gets an adequate amount of the proper food if you separate the two flocks.
Of course there are other ways to do it too, but the above is probably the most effective for most situations IMO.
Good luck, have fun,
Pat
