Where can I get a solid wooden block?

Good ideas, I’d go for the old college try and use concrete blocks. Spray paint them and decorate as you wish.

Why not just create a keep-out zone around the rack?

Having trouble seeing so just found the link in the OP. That’s a cool book rack. Wish I had one like that in my workshop. A real or manufactured stone pedestal would be great to prevent tipping if it could be secured to the base of the rack.

It’s an old model which I bought used, as I am fairly impoverished. Model is 670. I can schedule it via app and tell it to start or stop, but that’s about it - no “mapping” at all.

Don’t elevate, fortify

Put around the base of the book rack, probably could get away with just mating up the ends against the book case just to the right, no need to attach the ends together

Edit to Add: keeping it loose means you can easily protect your book rack when roomba-ing and throw it in a closet when not needed.

Put something black in front. Robotic vacs won’t move over a black surface.

I like the idea of a round riser. It’ll blend in better, and it seems like you’d be less likely to stub your toe on the corners.

This is another great idea, and a cheap one too.

Are you using Roomba in the generic sense? Uh, I guess I’m missing whatever point somebody else may or may not have made, but don’t you configure your robot vacuum to map the floor to be cleaned? With mine (which is not a Roomba), I can exclude it from parts of the floor, and I’ve undertaken to do that because — guess what — it always gets hung up under the legs on my keyboard stand.

Nope! It is an iRobot brand Roomba 670. I bought it used for $45 on eBay. It’s the lowest/oldest/cheapest model I could find that lets you schedule it to run automatically. I can create a weekly cleaning schedule for it, and I can remotely tell it to start cleaning, stop cleaning, or return home. That’s it, no mapping.

If I had hundreds or thousands to burn on it, I would definitely have got one that has mapping functions. But I didn’t/don’t.

I’ll bet that if you went to a place that does headstones you could get a nice piece of granite.