will adding outside office be worth it

[E. Raiola]

looking to finish a 18x12 shed on a concrete pad..it will have plenty of electricity ..finished drywall walls and ceiling...windows..beautiful matching outside finish...this will be in Cotswold neighborhood.. it will have heating and air conditioning...no plumbing no bathroom..  will this add value per sq ft any ideas how much more value...dont want to spend 8k and not get my money back thanks fellow investors