When it comes to building construction CAD, there are a lot of programs out there that do an OK job and are fairly cheap. Or there used to be when you could walk into BestBuy and buy software off the shelf...
I got much more serious and ended up using Chief Architect to design and make prints for my house and shop build. Nowadays it costs close to $3k, so I doubt that is an option you want for this, but I know they sell a stripped down version called Home Designer for anywhere from $100 to $500 depending on version. They also allow you to download trial versions, so you can give it a whirl before you commit. I cannot honestly say if the Home Designer series compares well to their flagship Chief Architect platform, but the higher end stuff was clearly good and very powerful, so I would expect the simpler versions would do what you want for a simple shop and carport. They do make Windows and Mac versions too, so that may be a big deal as I don't know how many are available for Mac. No connection to them other than a user (well, mostly a former user as I haven't touched it in a few years at this point). Download the trial and see if it does what you want. They had a lot of training videos for the flagship product, but charged extra for them. You might find some on Youtube for the DIY series.
DIY home design, interior design and remodeling software from the creators of Chief Architect. Create floorplans and visualize in 3D.
www.homedesignersoftware.com