Awhile back I wrote that I wanted to slipcover the sick couch. When the kids get sick they like to hang out on
this couch. It was looking pretty "sick"
I finally did it in mid July. I first bought two 12' by 9' drop cloths from Lowe's.
I bought the extra heavyweight ones and washed them in hot water. I air dried them, but they both shrunk at from 1-3 inches on the length and 8-9 inches on the width. A lot of fuzz also came off in the washer and the texture seemed a little rougher. I made tons of measurements of the couch and then drew the pattern pieces on graph paper.
This was helpful for the cutting layout, especially since each drop cloth was three sections of fabric sewn together. I over estimated with large seam allowances, but I probably was too liberal in that area. Sticking to the grain was also difficult. I would also advise using pins with large heads so you can handle and see them easier. Your sewing machine has to be able to handle thick seams.
It took me a week to get this completed. You need lots of patience to remeasure, recheck, and refit. I first pinned one side all together but took it out again because it was easier to sew and fit and pin each seam one at a time.
Doing this in the winter when the house is cooler would also be helpful. You have to ignore some folds, wrinkles, unevenness, and imperfections. I like how it turned out, but I am not ready to tackle a big piece like this again. I would also never do this with a pattern that would need matching or centering. I did use one of the original drop cloth seams centered down the love seat and it doesn't look bad. I like the neutral color of the couch, that won't compete with the pillows on it.
I would encourage you to look at blogs and websites that give tutorials and discussions on this if you are planning on tackling a slip cover.