Is your home new, fixer upper, or older home that buyer might consider purchasing only for the lot to build a new home on?
How big is the lot?
Does the backyard offer privacy?
Do neighboring homes have decks or patios?
You might want to contact a few deck construction companies for ideas and suggestions.
Do your research and if you feel YOU will enjoy YOUR HOME with the deck more, than build it. The chances are, the future buyer will appreciate the deck, as well :-)