Besides the second-hand skirt--a big full one--Re-Nest says we'll need this stuff too:
  • a second-hand pillow
  • pins
  • scissors
  • a sewing machine, although Re-Nest says you could hand-sew it, but it'll take a lotta time and patience
How to Turn an Old Skirt into a Rose Pillow - Rose Pillow - Pillow - DIY

For sewing instructions head on over to Re-Nest for the Cliff's Notes version or to the Examiner for the full tutorial.