The quality of plywood is dependent on two factors. First the type of bonding glue and second the wood used. Both "weather and boil proof" (WBP) plywood and "marine" plywood use the same rescorcinol-type waterproof glue. Other types of ply, with one exception, don't use a "waterproof" glue so must not be used for boatbuilding.

The exception is possibly the "best" plywood you can get, the Dutch made Brynzeel. Even though it doesn't use the "correct" glue and therefore isn't classified as marine ply it actually has a guaranteed life when used for boatbuilding far longer than most other plywoods.

In some areas, notably N America, it is possible to get marine grade softwood ply (usually douglas fir). Otherwise the choices are usually "Far Eastern" (meranti) or Gaboon (also known as okume). Of the two I recommend gaboon as it is significantly lighter than meranti. It may not be as strong, but it is maximum stiffness and minimum weight that are the main requirements for plywood, generally all boats are strong enough.

As a general rule, if you are not sure how to judge the quality of wood, choose marine ply, but if you are able to inspect the wood, or can get it from a reliable source then WBP is usually OK for decks and interiors. But I'd still use the real thing for hulls that are kept afloat (even if glass/epoxy sheathed) and beams. That is because one of the differences between marine and WBP ply is that although the outer veneers will be essentially the same for both standards, the WBP inner veneers can be in several pieces, have gaps and be of less good quality.

The choice of timbers appears at first to be more confusing, but can really be broken down into three main types.

First there is timber used for strip planking. By far the best wood is western red cedar. It is lightweight, easy to work and durable. However it has a short grain and is soft so should not be used for structural timbers. Sometimes this wood is unavailable and so you should consult with your timber supplier for the nearest alternative. But be aware that you boat is likely to be heavier if you use a different wood.

Second there is the timber used for general framing, stringers etc. The species of timber you can use for these applications appears to vary enormously, but in fact they generally all have similar properties and so are equally suitable. You are looking for a lightweight timber with a long grain that is easy to work, as knot free as practical, and that glues easily. Usually the softwood pines and firs are the logical choice. Douglas fir, yellow cedar, sitka spruce, are typical examples. Again, your timber supplier can advise you further.

You want to use "joinery quality" or better as that standard has the least knots. Unless you are sure of your supplier it is best to inspect the wood yourself, and certainly be allowed to reject any you feel is unsuitable. Generally though you can cut out and discard sections of poor timber. The only exceptions to this are gunwales and, in particular, beams, which must be best quality throughout.

Finally there is timber for cosmetic uses, including outer gunwales, galley trims etc. For these you want a hard wearing and "pretty" wood. So teak, iroko or other hardwood is the logical choice, unless you want painted trim of course.