People love cedar cladding because of its natural reddish brown colour, but left un protected it will weather to a silver grey as it is exposed to sunlight. If you want to preserve the original colour you will need to ask your garden office supplier to apply an ultra violet protector at the time of installation.
Not many garden office suppliers offer UV protection on their cedar cladding as standard, but most offer it as an optional extra. This is because some garden office buyers like the weathered silver grey. It is also a labour intensive process so does have a cost implication.
Millworks who supply cedar cladding to several leading garden office suppliers sent through some images of cedar with the UV protector applied and some cedar that has weathered for just a few months to see the differences:
The most popular finish for preserving the colour of cedar cladding is OSMO Clear UV Oil. Millworks recommend that 2 coats are applied to each board before installation. The oil is then reapplied as needed, this is typically every 1 to 2 years. The different elevations of your garden office will weather at different rates, dependent on their exposure.
SIPS Garden Rooms are a supplier who offer UV protection on their cedar cladding. There are several photos in their gallery on this site showing UV protected cedar cladding, here is a particularly good example:
Contemporary Garden Rooms also offer UV protection on their cedar cladding as the image below shows. You can see more examples of their cedar garden offices here.
These two images show that the UV oil adds a real richness to the cladding, by keeping it topped up you will be able to maintain this ‘new’ look.