Adding new topsoil to a yard that has already been prepped by a landscaper is a huge mistake. Your drainage is already established. When you add topsoil you will disestablish the drainage, possibly with catastrophic consequences. At worst you will flood your own house by building a dam up near it. Or you might flood your neighbor's house or yard. Even adding 1/4 inch of topsoil is a mistake.

You do not need new soil anyway. Straw is commonly used in a few parts of the country to cover new seed. Have you watered the yard (3x per day for about 5-10 minutes) for the past 3 weeks to try and sprout the seed? I've never heard of any other reason to cover a yard with straw. I would do the watering first.

If you think you have problem soil, you probably don't. Almost any soil can be fixed. If you bring in new topsoil, then you would have to fix that soil. Fix one or the other but don't simply bring in topsoil for grins. The easy way to get started improving the soil is to apply an organic fertilizer. This isn't just organic hype. Organic fertilizers feed the soil microbes which, in turn, improve the health of the soil. If you want to improve the efficiency and effectiveness of the soil microbes, you could get a Logan Labs soil test ($25) and post the results here. By correcting salt and/or chemical imbalances you can improve the environment where the microbes live and make them work better for you. But almost nobody has enough organic matter, so starting with that is never a mistake. I like to use alfalfa pellets (rabbit chow) at a rate of 15-20 pounds per 1,000 square feet. Spray to moisten and give it a day to swell up. Then rake over it or drag a hose or something to distribute it and knock it down to the soil.

If you decide to seed/reseed, then yes, rake the straw off. Scatter the seed over the surface, roll it down with a water filled roller to make good contact between the seed and soil, then start the watering. You don't need more straw. That just complicates it.

Now is a horrible time to seed new grass. Tomorrow is worse and it gets worse and worse until the end of July. Fall is the best time. I guess I should have asked where you live and what kind of seed you're planning before making this general statement. If you're planning to seed bermuda then now is a poor time, but it gets better and better until August.

I'm in Washington, and the builders don't put seed down so it's just rocky hardened dirt with about 3 inches of straw, according to them it's sole purpose was to absorb water so my yard didn't wash out. Also the yard very clearly slopes towards 2 different drains, if I match the slope do you think I will still have drainage issues?

If it very clearly slopes toward the drains, then they already set up the drainage. Adding topsoil will become a mess.

So they used straw as a mulch. Actually that was brilliant. The soil under the straw has become excellent. That happens naturally under mulch. Organic fertilizer is still needed, but the soil microbes have been perfecting the soil under the straw. About all you need to do is rake off the straw and seed, as I said before, and then seed.

When you say rocky, how big are the rocks and are they at the surface?

Are you in the wet part of WA or in the desert?

The wet part, and mostly on the surface so I could probably pick them all out, just a lot of work.haha one issue with going this route is the yard is sloped but is haste not been flattened, like you can still see heavy equipment tracks and stuff under the straw, what would be the best way to "smooth" it out without killing myself. I'm new to the homeowners club so I'm trying to get as much info as possible

The soil was compacted by heavy machines? Might be a bit of an issue causing a bumpy yard for a few years. Sounds like the new home construction contract did not include a grading and leveling in the final month of build?

Cheap route:

I would remove the straw, then remove all the rocks you can. Then I would aerate the parts where machines drove over the ground, others will tell you to spray baby shampoo from a garden sprayer, at least do one or the other or both. Soil test and amend based on advice here. Fall plant grass, probably perennial rye in your area. Yard will be bumpy for years if the machine tracks left it uneven.

Expensive route:

Pay a landscaper to properly do all of that, I think dchall can give you advice on how they are supposed to do it (box blade on a tractor?)). And ensure they grade/level into correct drainage areas.

Back a few years ago there was a golf course manager on this forum. One of his delivery trucks backed up to a storage building with an 18-wheeler and left ruts about a foot deep in his turf. He used a roller to push the high spots back down. Don't be tempted to add topsoil or sand to fix that. Get the soil fairly moist and walk/jump on the high spots. Or when the soil is dry, you might use a hoe to scratch the high spots off and push the extra soil into the low spots.

Can you please post a picture of the area? I have an image in my mind but I think it's from a different OP.