For DIY solution sheet aluminium panels for actual mobo bed, which then stacked with the help of m8 threaded rods with a thick and sturdy wooden base made of ply or board, then would have drilled mobo spacers/standoffs according to appropriate ATX standard or in case you want less space and using micro atx / mini itx boards then holes according to those
assuming you might not be putting in the same room where you work or something like that, i would use a big heavy duty table fan rather then many smaller pc case fans or like something that if the room being used doesn't have AC, rest setting and linking then up is on one's own requirements and ease of use
i can make some rough designs and walk you through them further personally