Building addition: cable runway recommendations

Panduit makes a wiremold rectangular plastic duct product in various sizes which fastens to the wall & has snap-on removable covers. There are competing products available; ensure that whetever you use, the cover is capable of being opened up again because you'll need to access inside occassionally.
You can also use this product for your AC power wiring but don't put your a/v cabling in the same duct. There's also a steel version available; not sure who makes that. Visit your local electrical supply house or larger hardware center for some ideas.

Don't use anything made of a magnetic metal for conduit. Keep any AC power wiring at least 6" away from signal cables(unless they can be crossed at right angles).

Idfnl,

Reading your post I assume you want to have the raceway/s concealed inside the wall and connect to some type of concealed outlet box with a finish wall plate.

Carlon Ent flexible conduit may be the way to.
You may also want to check the boxes they offer.

Something to consider is future technology down the road.... Once the wall studs are covered it will be costly to add additional raceways so make sure what ever size you use it will allow future fill space.

You also may want to have at least two raceway runs to each location. One for small signal cables and one for loads like speaker cables.

Don't forget them factory terminated ends on the cables.... Size conduits accordingly for the ends to fit through the conduit.

Wall stud thickness..... You may have to have the contractor build a double wall construction for the diameter size of conduit and outlet boxes you use.