Ensure you get 44" x 60" for standard 40k or Age of Sigmar. For smaller skirmish games like Combat Patrol or Kill Team , look for 44" x 30" .
Stick with 2mm to 3mm thick neoprene with stitched edges if possible; this prevents the corners from fraying over time. buy warhammer gaming board
Avoid overly "textured" hard plastic boards (like the older Sector Imperialis tiles) if you want to avoid "cocked dice" (dice landing at an angle) and loud clattering. Alternative: Modular Tiles Ensure you get 44" x 60" for standard 40k or Age of Sigmar