@rbrown #freecad can look intimidating at first but it's excellent for parametric modeling. Which I imagine you'd like to do, so that you can change the dimensions in a spreadsheet and have the model update it everywhere.
This is an excellent series for beginners https://www.youtube.com/playlist?list=PLWuyJLVUNtc0UszswD0oD5q4VeWTrK7JC by @MangojellySolutions. Good luck!
Edit:typos