Bought my garden office through limited company, couple of things our accountant told us;
It is being devalued over a 7 year period, so as long as you stay in the house longer than that it is then clear on the accounts
If the office is not 100% work use then you can get around the CGT issue, hence why I have 20% of mine for personal storage
TBH I think as long as you don't take the piss then you are probably ok with a home office in the garden, but wouldn't want to risk a permanent building (I looked into converting one of the barns here, but quickly decided against it).
The problem is that the CGT is payable by you the individual & home owner, not the company.
In that regard, it doesn't matter if the value of the asset has depreciated to zero (in itself a contentious issue, as I understand it) - the CGT is payable on a proportion of the residential property value.
Bought my garden office through limited company, couple of things our accountant told us;
TBH I think as long as you don't take the piss then you are probably ok with a home office in the garden, but wouldn't want to risk a permanent building (I looked into converting one of the barns here, but quickly decided against it).