You can make a Marudai out of any material that is very smooth and doesn't snag the threads. Any smooth metal, plastic, glass, glazed ceramic, or varnished wood can work.
The most important feature of a Marudai is the "well" - the slight depression around the center hole. The well gives the strands freedom to move while still keeping them under even tension. There are several DIY Marudai out there made of laser cut plywood or acryllic sheets or an old wooden stool with a hole drilled in the center, but all of them lack the well.
The strands form the braid in the space between the point where they touch each other (in the center of the Marudai) and the point where they drag the most against the surface. If the entire surface is flat (lots of drag) and there's only a small hole, that limits the space where the braid is actually formed, makes the braid uneven and not tight enough.
My personal recommendation is: If you cannot craft a Marudai with a well, craft one with a really big hole instead. A cross-section of some different shapes of Marudai would look like this:

What gave me the idea for my own DIY Marudai is this contraption of a lamp shade and a wooden plate by Ruth MacGregor Warnick:

Another variant is this Marudai by T3hJones. It has a wooden plate with a high rim that mimics the traditional well.

I've also seen people use a metal flower stand with a smooth, even rim, but I can't find the picture anymore.
Personally, I use this really big flower pot with a protruding rim. Here it is with my current braid and some colored stickers to help me not cross the wrong strands:

For my bobbins (aka "Tama") I cut a rubber tube into pieces long enough to push 2 metal nuts inside. Since my threads kept slipping off the sides, I added a rim of hot glue. They aren't pretty, but very practical and the rubber and hot glue dampen the clacking sound when they hit each other (or the flower pot) during braiding.

Left are the raw components of each of my bobbins: a piece of rubber tubing and 2 metal nuts.
In the center is the assembled bobbin with a rim of hot glue. The weight of each bobbin is 30 grams, which is less than traditional Tama but works really well for me.
Right are some spare bobbins tied together to form the counter weight that is clipped to the braid.