The first thing to do is to create a layout on the ground where the walls will go. Make sure the layout is square. You can use an inexpensive construction calculator to do the math or you can make your own 90 degree angles with common, known math solutions. For example, you can use ...
Grids are great if you’re not a slave to them–I like the 960gs, but I tend to agree that there are way too many classes that are required to make a layout work. From a design perspective, gutters should be as flexible as possible otherwise every design will start to look the same...