Are we talking height or width?
The tallest orchid I've seen is my
Vanda roxburghii f. aurea, which in the picture, stood about 8 feet tall a few years ago (I'm 6'1" for reference). I believe it is currently around the 10 1/2ft. mark, need to take out my extra-long school ruler... the roots are tied into a ball, and would add an additional 3 or 4 feet to it if they hung down!
The widest orchid I've seen was a
Eulophia species at Redlands 2 years ago, a massive specimen maybe 5 feet across (?) completely full of bulbs... it was an amazing plant, or perhaps a compilation of many plants.
-PM