I am not a fan of plastic myself. To me, wood wins hands down.
For a start, it is not as long-lasting. Urine can be very damaging to plastic, so if you have a tidy bun who wees in one corner but you don't use a litter tray that will cause a fair amount of damage. Also, plastic (believe it or not) decays faster than wood initially. Wood will rot, but that takes a long time. Plastic will become brittle, especially with exposure to direct sunlight, and will crack and break.
Secondly, the temperature issues. As people have said, unless you can avoid sunlight it will get far too warm in the summer when a good solid hutch wouldn't. Also, in the winter plastic would get condensation on the inside resulting in the rabbit having nowhere dry to hide from the cold... bring on the pneumonia! Eep :?
And I won't start on the price...
Cat