The sofa was my first large DIY project that required a fair amount of construction. It took me about a week working a few hours a day. I followed the plans as they were listed but made a few adjustments to accommodate for the size of the cushions. I used regular pine and then cheap lumber for the slats, lesson learned. Way too much sanding and it still didn't have the finish I was hoping for.
For the chairs: I used a mix of plans from the Bristol outdoor lounge chair (Ana's) and the simple outdoor sofa. I chose to use all sect pine for the chairs, after the hard time I had with the cheaper wood I chose to use on the sofa. I was much happier with the end result. I used 1x3's mostly and then added 1x1 composite molding as an accent around the base.
I looked long and hard for cushions before I started the project based on the recommendations from others. I took me a while but I finally found Somewhat affordable outdoor sunbrella cushions at Lowes. These are the Allen + Roth deep seating sunbrella cushions, which I highly recommend. They are very comfortable and dry quickly after it rains.