Boards are easy to cut and can be left untreated to weather naturally. Life span is easily more than 20 years. Both are expensive. Cedar sapwood breaks down quickly in moist conditions. Redwood and cedar are sold in all standard dimensions.
Redwood can take a few days for special orders.
For redwood, use kiln-dried deck heart or deck common. Clear heart, clear, B heart and B grade redwood are fine for lower budgets. For cedar, clear all heart is the premium choice. Twice as strong as oak, ipe is more durable than redwood and cedar. It has a life expectancy of 40 years or more, and is resistant to insects and decay.