Creating a home office

When building a home office there are a few points to consider:

• It is important to ensure the home office is not assigned exclusively for business use, as this could impact your capital gain tax if and when you sells the property. Usually, when a person's main residence is sold, any capital gains are free of tax under PRR (principal residence relief). If part of the property was used exclusively for business, it would not fall under the exemption and therefore part of the sales proceeds would fall under the scope of capital gains tax. More info here.
• Moveable furniture, such as desks, chairs, lamps etc. are allowable business costs, provided they are incurred 'wholly, exclusively and necessarily' for the purpose of the business. These items would become part of your company's balance sheet and the company can claim capital allowances on the costs.
• Immovable furniture, such as shelving, built-in desks, plug points etc would not be allowable business costs as they form part of the personal property owned by the director and cannot be taken by the company should it choose to relocate. 
• Design/consultancy work in designing the space is a bit of a grey area. Some may be able to be put through as a general consulting cost for the business, but this could be argued either way.

Once the home office is built the normal recharging of expenses rules apply.