Im sure everyone hre will tell you the best thing to do is kill those weeds from the root - round up / weed b gon, get at them now til fall. In fall then do the sod the grass will have a better chance.

Don't till the soil or turn it over, it will be lumpy and uneven when it settles and your sod will follow the contours. You can lay sod at any time, but it will do better when temps are lower, especially at night, and be less susceptable to disease. You will be watering daily with sod, and in the heat of summer this would also exacerbate fungal problems. Soil prep and condition is pretty important with sod because once the roots extend below the soil it comes with, it will need an environment that is suitable to support it. It would be a good idea to get a soil test now to see what is going on in your soil. If your soil needs corrections and amendments it will be better to do before the sod goes down. Personally I would kill everything with round up a few weeks before the sod goes down. When everything is dead, scalp it, core aerate, then power rake the yard. This will loosen up the soil, making it easier for the grass roots to take hold when they penetrate their original soil and water will be less apt to puddle in any low areas.

Not only will it be lumpy -- there is a good chance that you will stimulate 10,000 years worth of viable weed seeds into sprouting.... and that between Fall and next spring -- you will grow a 3' tall wall of weeds, small trees, and every flavor of wild grasses that ever grew in the area...

Thanks

John