If you are looking to build a legal collection, the best approach is to purchase the original arcade PCBs and use a ROM dumper to create your own backup sets—a practice MAME was originally designed to support.
Otherwise, remains the gold standard for DIY arcade cabinets, RetroPie builds, and low-power emulation boxes. mame 2014 reference set mame 0159 roms chds top
In a complete reference set, CHDs are usually provided in separate folders named after the game. Unlike ROMs, CHDs are not zipped. They sit in their own subdirectory within your ROMs folder. If you are looking to build a legal