Hi Ana
I would like to share my experience making this Outdoor sofa (see attached link). http://ana-white.com/2014/07/plans/outdoor-sofa-2x4s-ryobi-nation
The sofa is supposed to be made using 2x4 boards, but these are not a standard size in Australia so I substituted with 90 x 45mm pine boards. No other changes to measurements were necessary. I followed Ana's instructions and definitely recommend using wide clamps to hold the base when screwing together. I only had short clamps so was rather difficult keeping everything firmly in place when drilling the screws in.
Next step was preparation for staining. I used Cabot's pine filler to fill major holes, knots etc, then sanded lightly paying extra attention to the arms.
I stained using Cabot Exterior Varnish Stain (teak colour). This turned out a beautiful warm colour that I just love.
Finally the cushions....
For the base I purchased a 5inch thick foam single mattress (on sale $61 so worked out to be really cheap foam). I measured to fit base and cut using an electric knife - worked a treat! I had enough left over to do a cushion along the back plus two small side cushions to go along the arms.
Next step was covering the base and side cushions. I purchased some outdoor Decorating fabric from spotlight as sofa will be exposed to some QLD weather. For the base, I used a similar process to the Censational Girl box cushion cover using Velcro instead of zips.
http://www.centsationalgirl.com/2012/10/simple-sew-box-cushion-cover/
For the side and back cushion I made up 3 sides of the cover, then inserted foam and sewed the last end closed (cheating I know but just too awkward to do proper box ends).
Lastly, the throw cushions.....these were really easy I made envelope cushions from a single piece of fabric....once again no zips (hoorah!). They only took 10minutes each to make and look great. See tutorial below.
http://thehappyhousie.com/simple-speedy-stuffed-sewing-tutorial-diy-envelope-pillows/
My first build so extremely happy with the result!