How detailed do you need it to be? I'd create it using a continuous thin wall around the room with a vertical boarding material applied to it. This material should have a vertical boarding 'fill' applied to it so it shows up in your line elevations. You will probably have to put it on a different layer to the wall with a different layer intersection group, so they don't try to join.
To do the Base and Wainscotting, draw the profiles individually in separate complex profiles, and apply these to walls; these will obscure any lines below, beams don't do this as they can't have any sort of cover fill.
You might even try modelling the panelling and moldings altogether in one single complex profile, but this could potentially give you problems with how it displays on plan and it's interaction with the floorplan cutplane. Best to try both methods and see what works for you!
Hope that helps.