Beryllium uses to be brittle, so rolling and hammering would be difficult. If you heat the beryllium to ease the operation, beryllium will oxidise and become very brittle.
You might try to glue the beryllium sheet on a flat part. Cyano glue can be really thin. Then you mill the beryllium down. I would NOT grind it because this will produce powder of beryllium, and worse, of beryllium oxide, which is toxic.
Cleanliness is a big issue. You want beryllium for its X-ray transparency usually, and any pollution absorbs W-rays more than the beryllium base: oxygen from air, carbon from the glue and the cutting fluid, metals from anywhere.
I wonder if a microtome could have enough hardness and strength to cut beryllium. Probably not.https://en.wikipedia.org/wiki/Microtome
Please take care of your health.