How should I build an exterior door landing pad?
If you build the pad with concrete you may want to consider not making it out of a solid block of concrete. Instead form it up to create sides and a couple of steps as necessary. But then fill a large portion of the inner area with sand so that the top of the landing is 4 to 6 inches thick. A little re-bar in the sides and folded over to embed in the top can help keep the thing together if it cracks due to frost.

If you do live in an area with frost getting deep into the ground you should consider adding corner holes down into the ground (with re-bar up into the step portion) that can act as posts down below the frost line so as to minimize the heaving effect that can make a floating construction move around during the year cycle and also settle into a off level state over a series of years.

Wood can offer an easy alternative but you have to determine if wood has a look that you like. Also wood may require replacement in 15 years or so depending upon materials and conditions. Finally with wood, if a frost zone, it is a good idea to build it on treated posts that you bury to a depth below the frost line.