i want to put sod on my front law which has grass on it already but its patchy...will the sod roots root...or do i have to remove all the grass first

You need to remove the old grass first. Your new sod will have to be in contact with soil or the roots will dry up and die.

If my company were to renovate your lawn we would first spray the existing grass with round up, after that has died we would scalp the dead grass, bag & rake it. Then aerate the soil, then level if needed. Then we would sod, apply a starter fert, like 10-20-10, roll the sod so it is in contact with the soil, and water.

If you cant afford that you can skip the roundup, but anything less will not have satisfactory results.

Jeff is correct (the other two are not). If you just put sod on top of the ground without preparation or on top of old, patchy grass, there is a good chance that the sod will either die completely or only take root in certain places. I have seen poorly installed sod actually floating as the water goes through it and lays on top of the unprepared soil underneath (it was like walking on a water bed!).

To make the most of your investment (sod isn't cheap), rototill the entire area to be sodded (or turn the soil with a shovel, break up the clods), rake it smooth and as level as you want/need it, water deeply, then lay the sod down and tamp it into place. Then, lightly water the sod so that the roots start to get down into the prepared undersoil.

Watch it carefully for several weeks, watering only when needed. If there are any dead patches, it may be that the sod did not make good root contact with the soil or that particular part of the soil did not get sufficient water.

Fertilize only after the sod has had a chance to get rooted. Then, feed lightly with a balanced, organic (not chemical) fertilizer. Avoid high nitrogen chemical fertilizers like ammonium sulfate. From that point on, follow the directions for sodded lawns in most general gardening books and on line sources.

No...you need to till the whole area, rake it even and lay down the sod and use a push roller so the roots can get close to the soil. The key to success is to water, water, water.