How do I create my own random map pack?

I like to play with a certain degree of randomness and suprise, but find myself disliking some of the maps that appear in the random land map, full random or blind random options. Many tournaments use a specific mappack, some even with a random option in them as well. The best example to me was The Empire Collective Cup, which had "TEC Map Pack Light" and "TEC Map Pack Random".

How can I create such a random pack myself? Is it difficult? If so, is there someone willing to help me out in creating one? Looking forward to your answers!