Firstly, you need to find out the owner of this office. As you live in a community your president or administrator may give you that information but the 100% secure answer is in the Land Registry. It could be a common area which belongs to the community or a private unit. The Master Deed of your community contains a description of the common and private areas.
Regardless of who is the owner the fact is that this kind of alteration requires unanimity of the Owners’ Committee OC (all the owners voting for in a meeting).
The usual content of the ownership right is limited in a community by section 7 of the HPA
The owners of each flat or premises may modify the architectural elements, installations or services of their flat or premises, giving prior notice to the commonhold representative provided such work does not diminish or alter the safety of the building, its general structure, its external image or configuration, or prejudice the rights of another proprietor.
The owner and the occupant of the flat or premises shall not make any alteration in the rest of the community (Common areas)
‘General structure’ means bearings walls and floor structure. ‘External image or condition’ refers to everything regarding facades or even canopies
Limits established in this section will not operate if an owner obtains unanimous consent from the OC