What I generally do is plot points (vertices) on the three grids and move them around building faces as neccessary. This doesn't include doing calculations and measurements. If you don't want the calculations and measurements, just plotting points and getting the basic size (given your map scale) is all you need. Choose your map size wisely (16:1 (16 quants to 1 foot) is common for FPS games, I use 8:1 for my 3D game and a screwy scale (but for a reason) for my 2D game about 75% done.