The shelf in the first picture is made of red oak plywood. You can choose the wood type, color and design as you like for your project. In case if you need more help understanding this project, you can refer the source link below. It discusses various items used, steps and tips and personal experience of the author who personally built a Zigzag shelf.
Hardwoods are separated into two categories, temperate and tropical hardwoods, depending on their origin. Temperate hardwoods are found in the regions between the tropics and poles, and are of particular interest to wood workers for their cost-effective aesthetic appeal and sustainable sources. Tropical hardwoods are found within the equatorial belt, including Africa, Asia, and South America. Hardwoods flaunt a higher density, around 65lb/cu ft as a result of slower growing rates and is more stable when drying. As a result of its high density, hardwoods are typically heavier than softwoods but can also be more brittle. While there are an abundant number of hardwood species, only 200 are common enough and pliable enough to be used for woodworking. Hardwoods have a wide variety of properties, making it easy to find a hardwood to suit nearly any purpose, but they are especially suitable for outdoor use due to their strength and resilience to rot and decay. The coloring of hardwoods ranges from light to very dark, making it especially versatile for aesthetic purposes. However, because hardwoods are more closely grained, they are typically harder to work than softwoods. They are also harder to acquire in the United States and, as a result, are more expensive.
Cedars are strong, aromatic softwoods that are capable of enduring outdoor elements, the most common of which is the Western Red Cedar. Western Red Cedar can sustain wet environments without succumbing to rot, and as a result is commonly used for outdoor projects such as patios, outdoor furniture, and building exteriors. This wood can be easily found at most home centers for a moderate price.