You can definitely design home office space yourself if you make and construct a nice plan. A plan must be made into a full details with all the features of the interior you will want to add to the room. It is quite possible that you are changing or remodeling the home office interior because the old one was not very useful, you are considering adding more furniture to the space because your documents easily get lost here and there. For securing special documents and papers, you need extra space, for you are considering making some secret cabinets. But do not what else to do, how to have the cabinets. I suggest that you make a corner style cabinet with racks, drawers and safe, the corner style racks or cabinets do not take much of the room space, allowing you have more rooms for the office furniture.