If you need to store stuff in your attic, here is one way you can build up the floor and install OSB or plywood. If you have insulation, typically it should be around 12" tall and insulated. It's important to not compress your insulation.

Steps
1. Install Floor Joists and Blocking
2. Install Plywood Floor

Attic Ladder DIY Solo Install Video
   • Attic Ladder DIY Solo Install - 5 Eas...