How do i install bead board in a small bathroom? Do I make a pattern of the walls??

A beadboard (wainscoting) is one way to go. But, the size they sell in the kits is only about 3-1/2 feet high (you did not say how far up the wall the faux marble goes).

First install the baseboard all the way around the room (or wherever u r installing the wainscoting). There is a notch at the bottom of the chair rail & top of the base board that the panels fit into. By installing the baseboard first, u ensure that the panels r the correct height to be covered properly by the base board (the panels just slip into the notch at the top of the base board when installing them). Do not forget about the 45-degree cuts (or whatever it comes out to) for the corners when u cut the baseboard to size. You can make the 45-degree cuts either with the Skil saw (adjust the blade to 45 degrees) or with a miter box & backsaw.

The panels r about 16 inches wide. They also have a tongue-and-groove joint between pieces. Start at one corner that is the most conspicuous & cut the groove off of one piece. I used a Skil saw with a 200-tooth blade, & used C-clamps & a 1X4 to fashion a guide for the saw to ensure a straight cut (very critical). If the walls r crooked, u might have to make a crooked cut to make the joint flush while keeping the top of the wainscoting level. If u experience chipping of the finished surface when cutting, put a strip of painter is tape along where the cut will be made (you will make ur cutting mark on the tape).

Attach the two beadboard pieces that make that first angle using Liquid Nails or some other paneling glue. Allow it to set a little bit, because these corner pieces r what the rest of the wainscoting is going to key on & u do not want them to move.

Now, just work ur way around the bathroom, putting up a new panel & cutting to size as necessary. When all the panels r up, cut & place the top rail, gluing it into place. When it is all done, u might want to caulk all of the joints with a white latex caulk. This hides all of the imperfections in the joints, or between the top rail & the wall, & gives it a nice clean look.

BTW - If the marble stuff is plastic, I would think it should be fairly easy to cover. If u sand it with about 60-grit sandpaper (using an orbital sander), that should gouge the surface significantly enough for a primer to stick. For the gaps at the joints, u could use a spackling compound to fill them in & then sand with the sanding screens they make for sanding drywall (it does not get clogged up with drywall dust) to smooth them out before priming.

Then prime & paint whatever color u want.

I put beadboard as a wainscoting in my bathroom. I simply measured the wall, where the outlets were, tore out & replaced the baseboard & capped it with a chair rail. Lowes does sell a kit that comes complete with the beadboard, chair rail & baseboard, but u have to check if the dimensions will fit in ur application. If not, they sell all of the wood items u will need separately. If u buy the the large 4 x 8 sheets, bring ur dimensions & they will cut it for you. While u r there, pick up some Locktite because u will need it to adhere the beadboard to ur plastic walls (it has the fastest grab & will adhere to slick surfaces). Plus, it eliminates the need for nails on the baseboards & chair rails. If u r putting the beadboard over the entire wall, u will need a little molding to put along all of the edges, like 1/4 moulding for the sides & a crown molding for the ceiling to finish it off. I suggest priming & painting the raw wood prior to hanging because it is easier & u will only have touch up once its installed.