A lawn grown from seed is a lot cheaper than laying sod, and in the long run it will also be healthier since it adapts better to the area. Plus, if your yard doesn't get much sun, shade-friendly fescue seed may be your only option. Given that sod is farmed in full sun conditions it will struggle to stay alive under such circumstances.
Fall is the best time for seeding a new lawn or patches that need special care. Why? By then trees have dropped their leaves, so seedlings get more sun early on when they need it the most. They will then go dormant in late fall and wake up in time for spring to arrive. At that time the sun will be high and the tree leaves will not have developed, so they'll have another chance for a growth spurt.
Before you plant the seeds, you'll need to prepare the soil by breaking it up with a rake. Remove any big clumps or dips where water may collect and then add a 10-10-10 fertilizer. Apply seed with a spreader and keep the seeds moist until they germinate. Continue watering regularly until the ground freezes but wait to mow until spring.