Cooktop as print bed

Has anyone looked into cutting down an old ceramic cooktop as a printer bed? The glass-ceramic material has near zero CTE, so it won't warp or shatter from heating, and there's a free, eco-friendly supply of large pieces from junked stoves. Any idea if the underside is flat, or how difficult it is to cut? Thanks.

Cutting via abrasive methods such as a tile saw should be easy. Another option would be borosilicate glass but it's sorta pricey compared to free for junked stove tops.