Grass can grow in rocky soil, but for a trafficable lawn getting the rocks out of the way or buried would be a good idea.

When laying down the extra soil just be aware that you don't want to alter the grade in such a way that your site drainage is adversly impacted.

Take this with a grain of salt as I am not an expert, but I'm not sure it's possible to do random sheet composting over a whole yard in one season (whole leaves gather in drifts when you "let them fall" and won't have broken down much at all in one season, especially not randomly on the ground), so if you are going to need significant topsoil for your lawn, you should perhaps just figure out what you need and add it. Plus, "straw", depending on what you use, may contain a lot of seeds that is just the opposite of what you want if you are seeding a new lawn. If you are talking about a more confined area, then you might be able to sheet compost yourself to some good soil by using shredded leaves and keeping it moist over the winter.

I thought I would use straw 1 yr for mulch! Local"have everything you need hardware store" just loaded the last bale on lady's truck for her horses. I asked when they were getting more in.It would be couple of days so I asked it I could gather some of leftover straw & try it to see if I liked it. He said sure, no charge. I gathered it up & got it home OK but as was spreading it around I got very clogged up. Seems I'm allergic. Then I remembered my DD(adopted) so didn't have my allergies, had to dig for prize at a Fair in a pile of straw, next stop was drugstore for Benadryl! So dumb idea as she would probably get problems even tho several yrs had gone by. It was a mess getting it picked back up. Now I mulch with lawnmower clippings, no cost & doesn't make anyone sick. So if asthma, hay fever or other allergies at your home don't invite trouble.

you can seed your grass before winter and allow it to sit under the snow..it will sprout in the spring with all the snow melt.