Illustrator :: Floor Plans - Creating Walls Quickly And Precisely

I'm a 3D artist but recently, due the high demand, I'm learning illustrator for the sole purpose of making floor plans (the artistic colorful ones), I know Photoshop very well and use it extensively, it would certainly be enough if I wasn't going to print the plans at various dimensions, even using smart objects and vectors I don't think Photoshop is the right tool for the job.

I've downloaded illustrator and so far I'm liking it a lot, I believe it's the appropriate tool for the job. However, I couldn't find a quick way to draw the walls precisely.

The biggest problem is I couldn't find a way to 'offset' open paths quickly... when the path is open, it offsets the lines to both sides, as opposed to closed paths, the way I found myself is to use the pathfinder to divide the offsets than delete the ones I don't want, but it's a pain, it's better to just draw both sides of the walls separately instead, what is a tedious process too.

I'm looking for simple ways to either offset open paths to a specific side, or maybe make strokes that are adjacent to the paths so i can use the 'outline stroke' tool to convert them to 'solid' paths, or any other way to achieve the same result.