The standerd length is around 42 inches now this in relation to bode size and weight is much the same as stand-up however you also have speed and bouyancy to account for.
Longer and wider = More bouyancy but less manoverability. So ideal for theose phat days where waves are very powerfull but are long and fat.
Shorter = more manoverability which is what you need on some of the stupidly fast and sucky waves that boogers ride.
Materials, Vary greatly. Decks and slicks are pretty much standerd with varyting rockers on the slick (underside) and channels to allow tighter lines to be held on waves, but its what goes on inside thats also makes a board. Different cores based around polypropalines and strengthening rods from dow carbon fiber and other TM'ed materials will set the degree of flex in the board. hotter climated need reinforment as the boards heat up in the warmer waters they flex more kinda like different wax temps.
The board shape, Tail ends are the main vairations in shapes.
Two main shapes:
Bat tail - Mainly designed for prone riding allows the hips and waist to sit into the coarner of the board to make tight turns on steep faces.
Crescent Tail - The choice of DropKnee (DK) riders. but also used for prone. Good all round shape.
Nose shapes vary again but not so much, wider noses are good for DK as more space to work with. Just a little more on flex of a board, depening on the riders style this will be personalyl choese accordingly like much of the other features, (tail shape, deck and channel set up etc) For me personally i tend to manover aggresivally on the waves so i like my boards fairly solid ad i'm bending them all over the place to make sections and torting the board with my body against the wave.
Its only a very general overview but if you give me some mre info or if you have more questions, I'll help you out no probs.