Cheapest/easiest way to scan/design for wheelchair ramp

Hi everyone…
I’m in my first couple of days with 3d printing, and I want to do something nice for my wheelchair bound mom.
When exiting/entering her house, the doors threshold presents an obstacle… nothing that she can’t run over, but it jostles her something fierce because of the profile of the door. I want to scan the threshold and make a set of ramps that will make it as smooth as possible without interfering with the door.

So a couple of questions… can I do something like use the LiDAR camera on my iPhone to take an accurate scan of the obstacle and then import that into a piece of software to help design the Ramps easily? It would need a decent amount of inner structure to support an electric wheelchair plus her.

If it’s easily done, what scanning software is out there (ummm free would be nice if it exists), and what would people recommend as the design software for a complete beginner?