In most cases, at least in houses built during the past fifty years or so, panels comprised of drywall have been used to cover the walls and ceilings.  Drywall is also known as wallboard, sheet rock, and gypsum board -- the latter because, to make drywall, there are paper facings layering a middle layer made out of gypsum.  There are types of drywall which are waterproof as well.  They are known as green boards, and can be used in the bathroom, as well as other parts of the home which are given to moisture and dampness.  Since drywall is so frequently used, the installation is a rather common task.  It is not as messy as, say, plaster, plus it does not cost as much as wooden paneling.  As well, once it has been installed, it is rather easy to design and modify drywall to suit your needs and tastes.

Typically, when a drywall contractor makes a bid on a job, the bid will take into account the size and area of the job, charging extra for any special finishing.  When considering a contractor, you should talk about the different options available to you and see if you can look at any completed samples.  That way, you will understand everything you are getting and there will not be any surprises or misunderstandings.  As always, try to get quotes and estimates from a number of companies, so you can compare pricing and quality.