If you want specific information on the building materials, go to the pages.
Building materials are necessary for basic defense of even the smallest bases. You need an entrencher to pickup and move materials. Materials include: Stone Walls, Stone Blocks, Bricks, Timber, Wooden Slabs. and Wooden Planks. Floodlights can be used in your base, however cannot be made into a wall or floor. Therefore I will not consider it a building material.
It is very effective for mobile cover, blockading doors, making roadblocks, bridges, and of course, walls. Be wary how much you use these, as if you move one as a raider, a giant breach has been made inside your base. It is recommended to only use stone walls if you are using it for a gate or for a bridge.
Block shaped stone. I find this is useful for blocking off double doors, as all four will completely cover the whole door. It is also effective for covering up the hole that lets people go up the stairs onto the second floor. Always board up from the inside. It is sort of big, so it is not recommended to use all the time.
I don't usually use this, except to make safety railings. It takes 3 inventory slots and is bright pink, making it easy to spot your base from far away. It is only recommended to use inside your base.
Essentially long, wooden bricks, it can be used in the same ways as bricks. If you are making a bridge you can use timber as railings or pillars (If you want to be realistic), or one of my favorites, use it to line stone walls when making long and tall walls. You don't have to, but it makes your base look good, but is also purely aesthetic.
These are the second best materials to have on hand. They have the same uses as wooden planks, but they don't have the same size. However, these are very useful for barricading doors and windows, and especially useful to line the top of buildings for cover. It's thicker size can make it the best material for ladders.
There are many uses for wooden planks, even if it is a small hassle to move and place them. It can be used to blockade doors, board windows, as a floor for a bridge, as a railing for the bridge, as cover for your rifleman when defending bases. You think of it, planks can probably do it. This is, in my opinion, the most important and the most versatile building material as of yet.
The entrencher is necessary and the most important tool in base making. In game, in inventory, and in hand, they all look like a metal shovel with a green handle. If you happen to come across one in your survival, pick it up. It is arguably the most important tool for large and even a small group. Surviving for long periods of time in one place will be a challenge without this.