Floor technique tutorial
The technique is rather easy. You just need a lot of grill tiles, a few 2x3 plates and several 1x2 and other 1xY tiles, along with a simple SNOT base. The size of the base is variable and the number of panels you use is totally based on how large the floor should be. I don't know exactly how many panels make a certain number of studs in length, so you just have to try it out, if you are building larger or smaller than this.
I hope this tutorial helps. Please, let me know, if you want to see more instructions like this for the techniques I use.