I originally planned on using 8 foot lengths of 1/4 inch thick planks of wood, but found some Wainscot Plank Paneling on clearance for $4.70 a package. The wood I was looking at would have cost $10 per package for the same coverage. I knew that ultimately the project was going to be painted and using solid wood really wouldn't change the appearance of the wall so I went with the Wainscot.
Here's how I did it...
To start off measured the area of the wall and made sure I had enough planks to cover the area plus have a few spare planks. My wall was 8 feet wide, 8 feet 3 inches tall at the tallest point and 4 feet 3 inches at the shortest point so I figured my supplies on an 8x8 foot wall. I also purchased four eight foot 3/4 inch thick 1x3's to trim out the wall.
Since I was working with a sloped ceiling I had to first figure out the angle of the slope the best I could before I cut my planks. To do this I grabbed a scrap piece of 1/4 inch triply underlayment, had my husband figure the angle as best he could mathematically, and then cut several angles to see which angle fit the best.
Once I found an angle that I was happy with I got to work, working each section from the top down so that my final cut for each section was a straight cut. For the very first piece I cut one of the planks in half and then cut the angle. Since my walls were not plumb or square I had to line up all of the pieces before attaching them to the wall to make sure that everything lined up correctly. Once I was happy with how things were lined up I used a pencil to mark where I wanted things to line up and nailed each plank to the wall using a nail gun and 2 1/2 inch nails. To finish off the first section I measured the distance from the floor to the bottom of the last plank and then subtracted 1/4 inch so I had room to work with. I used the left over from the cut for the last piece of each section to begin each new section.
I had one outlet that I had to work around. To account for the new depth of the wall I added an extender which was pretty simple to do. My husband made sure the power was turned off to the outlet, and unscrewed the outlet from the original box. I then slid the extender over the outlet and fit it inside the original box and then used the new screws to screw the outlet back into place.
When I got to the final section I had to measure and rip down the last little bit.
My next step was to install the trim. I wanted the corners that met the ceiling to be mitered, but wasn't worried about the bottom because I knew I was going to cover the bottom piece with the original piece of molding. Finding the right angle to get a tight corner was not easy. The only tip I can give you is to test cut the miter on some scrap material that is the same thickness and width as the material you are using to trim the wall. Don't cut your real trim until you are happy with the way the two angles come together.
Caulk did a fantastic job of filling in the gaps, I just had to make sure to mask the wall and ceiling off and take my time. I started by filling each gap halfway wiht paintable acrylic caulk and then smoothed it out with a wet sponge. Once it was dry I came back a second time and did the same thing, but this time I pulled my tape as soon as the caulk was smoothed so I didn't have trouble removing it after the caulk had dried. I repeated this step one more time and on the last time I used a credit card to smooth the caulk so that the final application was flush with the trim. I added my baseboards, applied a final application of caulk to everything, and finished it up with three coats of paint.