I've never been good at calculating bends. Otherwise, any 3d modeling software works. You could just use cylinders instead of empty pipes if that doesn't matter.
Do-It-Yourself, Repairs and Fixes
Share tips and tricks to keep people from throwing out that broken item. Repair before replace!
Dimensions and a cad program?
??? Blender? :D it may be a pain in the ass, but you can certainly do it with blender
There is FreeCAD and Fusion 360 available for free on the web. I believe Fusion 360 only limits you on the total number of projects you can have active at once. FreeCAD is free, but I found it to be a little harder to use than Fusion for some things. FreeCAD has good tutorials to get you started if you go that route. Idk if Fusion has tutorials, I already knew how to use Fusion before jumping in. Best of luck!
Tinkercad is another great tool
I'd use blender, but only because I know it better than cad programs
Sketchup is pretty decent and there should be a few browser version on their website. It's super simple to use as well if you're just going to be drawing a basic structure you'll only need like 3 tools.