You can make em just about whatever you want. Mala will scale images to fit.
The game list can be anything from huge fonts down to 6 pt type if you wanted it. Just depends on the visual you're after. Mine has about 8 games in the list and it stretches from the top of the screen to the bottom. but there are lots of layouts that have 25 or so games listed on screen at once, and take up less than 1/3 the screen to leave room for cp and cab images, and videos.
You might search around here and on the wiki for Mala layouts to get an idea of what's possible/typical.
My suggestion is mock up what you want in photoshop, fireworks or some other vector drawing tool, then clip the relevant portions out to create all the jpgs for mala to use.