If his new workshop is a different building, then you can't claim it as a home office. What you can do - claim your existing square footage for your business, as you did before, and square footage of area which was used for business in your husband old place as his home office. Set up a new building as a new business asset, you'll be able to take depreciation and amortization deduction for that.
You can find more information here:
Taking Business Tax Deductions
