I'm thinking of making a monolith from 2001 from scratch, as I have got some superbly black paint that almost eats light - not quite Vantablack levels of blackness, but not far off. I'm wondering what material would be best to use as the substrate for the monolith discovered on the Moon would be. I know the proportions are 1:4:9, and in the book the actual size is stated as "11 feet high, and 1¼ by 5 feet in cross-section. When its dimensions were checked with great care, they were found to be in the exact ratio 1 to 4 to 9—the squares of the first three integers." (some slightly iffy maths, I believe?) so what's best material to get that crisp squareness of the edges and parallel surfaces. This is a list of the methods I've thought of so far.
I could fabricate one myself from styrene, but getting it perfectly square is going to be tricky, and the edges are likely to be soft.
3D printing would be slightly harder in some ways, as although it's a simple shape, most 3D printed items need lots of priming and sanding to remove the tiny ridges between layers. That could again lead to softer edges and not-so-flat planes.
Milled metal or modelling material. This probably the most expensive method that would give me the ultimate in shape with lovely smooth edges and parallel/perpendicular planes, but it's also probably the most expensive and I know not where to begin looking.
There are a couple of "models" of the monolith available, but I'm loathed to pay £22 for a small bit of plastic from China, and the shipping of the slightly larger one would be ridiculous. They're also mass-produced, and I have no idea whether they'd be crisp enough for my needs.
Any other ideas, suggestions or "I know a guy" comments are welcome