When it comes to buying or building a skimboard you have to look at two basic categories, wood and foam.

Wood Boards

Wood boards come in a variety of shapes and sizes and are made of all different kinds of woods. They are cheaper ($60+) than foam boards with good reason, wood boards are very hard to ride in the water. Because the boards are made from wood they are extremely heavy. A small wood board may weigh up to 20 pounds which means that you sink when you hit the water. Wood boards tend to be more popular on the east coast where the beaches are flatter and much of the skimboarding that people do takes place only on the sand. This isn't to say that you cant ride waves on wood boards or on the east coast. It's just harder and takes more practice.

Foam Boards

Foam boards on the other hand tend to be very expensive ($160+). There is less variety in shapes and sizes mainly because the designs are well tested and the people who make foam skimboards know what works and what does not. Foam boards are very popular on the west coast and in Hawaii where skimboarders ride waves more. In fact I have been skimming for 10 years and have only personally seen a handful of wood boards. Foam boards are light and buoyant. My board weighs just over 3 pounds. Prices for foam boards start at around $170 and go all the way up to $300. This is because the materials are more expensive and they are harder to make. All things considered, if you plan on trying to ride waves, you need to consider investing in a foam skimboard.

The Properties of a Skimboard

There are five main aspects to skimboard design; shape, thickness, rocker, rails and weight. All of these however only make a huge difference when you ride on the water. If you are only riding on the sand then none of these are extremely important.

Size & Shape

Obviously a bigger skimboard is going to float better than a smaller skimboard but there are also other considerations. You want make sure and match the size of the board with your weight and athletic ability (i.e. how fast you can run). Boards that are narrow tend to turn quicker but do not carry as far over the water. Likewise boards that are wider in the middle tend to go far out in the water but not turn very well. Also boards that are shorter tend to offer more front to back control.  More important than the boards shape however is it's overall size.  A larger board will turn slower but go further and faster.  Likewise a smaller board will turn on a dime but you may have trouble reaching the wave!  For more information check out the board size section.

Thickness

Rocker

Rocker is the amount of curvature in the nose of the board. The purpose of rocker is to help you make the transition from the sand to the water as smoothly as possible. Obviously a lot of rocker would be desirable for this purpose but unfortunately too much rocker makes a board slow. Rocker is one of those things that varies a lot from rider to rider. Its all personal preference. On the east coast 2 inches is common while on the west coast 3 inches is common. This is because the beaches on the west coast tend to be steeper therefore requiring more rocker.

Weight

The weight of the board is pretty easy to figure out, lighter is better. It is possible to get a board that is too light especially if you live in a windy area but in general just get the lightest board that you can. One other consideration is that in extreme cases the board may be light due to the fact that the fiberglass is not saturated enough, if your making your own board be sure and use enough resin.

Tail Shape

Skimboards have many different tail shapes.  The one pictured above is one of the most common, a pintail.  Pintails help a skimboard to be very stable in the water.  Other common tail designs are swallow (W shaped) and square tails.  Both of these tails give a board more manueverability in the water.  By using one of these tails, you effectively shorten the board.  This gives the board a twitchy feel because front-back mobility is less constrained.  One benefit of swallow and especially square tails is that they throw a much bigger spray.