The way I just did my full size plan, was draw it small, and get it RIGHT
Then draw grid lines on the paper and make sure they are all perfect squares
Then scale it out using the nut measuring technique or what ever you want to use, and draw bigger squares on a larger sheet of paper, and have the bigger squares be proportionaly ratio-ed (is that a word?) to the smaller ones. And then just go from there, drawing one square at a time. And sketch it lightly, and get a good eraser (you will need it)