The cost of any home improvement is added to the cost-basis of your home and may reduce your capital gains when you sell the home.
Then, you could possibly claim a home office deduction for the space, if you met all the rules, but even then the most you could do is claim a deduction for depreciation over 27.5 years, which has to be paid back when you sell the home. And you don't qualify for the home office deduction unless you are self-employed, AND the office is your regular place of business, and you use that sunroom exclusively for work and no other personal uses.
