Side and rear fences can be 2m tall without planning, but front ones are restricted to 1m
Often people just go for it and are not caught with garages, extensions, fences etc, then if its been there for more than 5 years they cannot make you tear it down.
Choice of material is irrelevant, a garage is a garage, and requires planning unless its at the side or rear and meets a number of criteria.
Once you contact planning they will keep and eye out, you might be better off getting a sectional garage then at least its easy enough to dismantle and sell on if you wanted to take the gamble.