What's the easiest way to make consistent simple walls? Blender beginner here. I imported an image of a floor plan into Blender, aligned it with the grid, scaled it so one unit = 1 foot (it's from the 60s so Imperial). But I'm having issues making the walls:

First I tried putting a loop cut in my first wall and extruding it, but I don't know how to make a cut that's exactly the same width as the existing wall.

So then I tried copying and pasting the first wall instead, rotating it 90 degrees, and snapping it to the first wall. But it doesn't want to snap even though I turned on snap.

Is there a better way to go about this process?
Solidify modifier.

For recent builds (2.82) with the complex mode 



Consider using the solidify modifier. Model your walls as simple edges on the plan.. When done extrude to wall height to. Add a solidify modifier to give walls thickness.

Fiddle with settings, for example making offset negative half thickness will keep original edge mid wall.