This is a small design, nothing much to it, its incredibly simple to make and doesn't require many materials so you don't have to go material hunting if you want to make this.
Start with a 4x2 base and place sticky pistons in a 2x2 formation facing upward
After the foundation, add two slabs on the higher side of the lower pistons, and place two redstone pieces on top of them.
Add a block above the slab with a redstone torch behind it, do this on both sides of the pistons.
Add two other blocks on top of the redstone torches, believe it or not, thats all you need for the redstone wiring, simple.
For almost the final step, add sand blocks in a 2x2 formation on top of the pistons as well as adding two blocks infront and one above of the 2 slabs.
Add the lever and your floor and badda-boom, you got yourself a working sand door, make sure not to press the lever too many times.