Choosing your own timber for an outdoor deck or furniture project can always be a good thing, as you can ensure you opt for quality wood that has the look you want for your project. When you are ready to pick your own timber from a lumberyard, you may be a bit overwhelmed with all those choices, but remember that not all wood is alike. Different species and different treatment to timber products can make some pieces better than others for your project and can greatly affect its longevity and appearance. Note a few tips for buyers who are looking to pick their own timber.
A word about defects
Defects in wood can actually be very attractive for a project; knots and other lines in wood give timber a very rustic and natural appearance. You may actually want to find these when choosing timber for a table, cabinets, and the like.
However, avoid defects that could compromise the strength of the wood. This means anything that might affect the wood's thickness; a knot that has settled and pulled away from the wood's surface might make it weaker in that point. Twisted wood or wood that is warped in any way, called cupping, also typically won't be as strong as wood that is perfectly straight and level, even though it may be cheaper. Don't choose wood by price alone but be selective about wood with defects.
Some species of wood are actually more naturally resistant to moisture than others. Oak, walnut, and cedar are denser so they absorb moisture more slowly than species like Douglas fir. For an outdoor project, you want a wood that will resist moisture as much as possible so the wood doesn't rot or hold mold and mildew. Even with a sealant and regular maintenance, it's good to avoid species of wood that might get soft over time because of absorbing moisture.
Note finished measurements
When buying timber, note that the finished measurements may be different than wood that has not been planed, or dressed and sawn. Dressed and sawn wood has been sanded or otherwise treated so it's smooth on all sides, but this reduces its overall measurement. However, a lumberyard may note its original measurement versus the finished measurement, and this could mean wood that is slightly smaller than what you need. Look for finished measurements on finished or treated wood so you know the size you're getting.