Building a deck without help
A lot depends on what you are building. There are two different types of decks:

Traditional Deck

This involves (typically) some sort of footings to hold the posts, a ledger board on the side of the house and a lot of very specific rules designed to make sure the deck doesn't fall down and hurt people. The deck has to be extremely rigid - you can't have it move away from the house.

Floating Deck

A floating deck (typically) has posts fit into specially designed blocks:

which simply sit on the ground. The entire deck may move a bit over time. As a result, there are limits (which may vary by jurisdiction) as to the maximum height and other constraints. But a big difference is that you do not attach the deck to your house. That actually removes a lot of the usual concerns about how everything is connected together. End result: a floating deck is much easier to build than a traditional deck.
In some cases, a floating deck may not even need a building permit, which is a big advantage. However, that is dependent on jurisdiction (in my area, OK up to 200 square feet).
Check with your local building department (county, city, etc.) and find out if a floating deck is permitted and, if so, what the constraints are. That may go a long way towards making this a one-man project. I built mine (&lt; 200 square feet, very short posts) together with my evil twin. I could have done it myself, but an extra set of hands is really useful when you are placing 10' or longer boards.