Desk Top, not so much as fighting class but general size comment on robotics building... rather than floor or garden rover, people carrier or ginormous beast.

Like you say small can be quick to build, there's common shapes but that's not necessarily what gives a competitive edge. I like mini-sumo 'cos it's got a low cost of ownership, damage tends to be your own stupidity and you really don't need much of a workshop to get you going.