Typically you have a stud every 16 inches. This means you need 12 for the 8 foot sides and 16 for the 10 foot sides, for a total of 24 studs. On the drywall, assuming you have 8 foot walls, you will 4 sheets for the 8 foot sides and 6 for the 10 foot sides for a total of 14 sheets. This does not include the 2x4s for the top and bottom of the walls. The number needed here will depend on the length of the ones you buy. You may also want to buy some extra of both because mistakes happen.

Are there windows, doors? do you need nailers for the ceiling? don't forget the corners? Are you running single or double plates if a bearing wall? are you rocking the ceiling? My estimation would be 45 to 50 but I always would rather have to many than run out plus I use them all the time so they dont go to waste. You can bring them back alsobut draw a simple plan or be able to answer these questions and give HD or Lowes a call they more patient with DIY'rs ask for lumber or building supplies and they tell you exactly. If I were you I'd buy 10 boards for your 10' walls also a 2' butt joint is just extra work for nothing. The light weight material cost a couple bucks more but in a house I love it for light work, good luck

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