In reply to TN:
Hope I'm not teaching anyone to 'suck eggs' but if you are planting grass remember a few points:
1, make sure the soil is at the correct pH and that P & K levels are correct (Phosphorous especially)
2, make sure you plant a suitable species that will take heavy trampling (Golf courses and playing fields will use these). You might find shade loving species for the areas where tree cover is a problem.
3, Grass seed is very fine so you need a fine and COMPACT seedbed, best to roll it with a heavy garden roller.
4, Soil moisture (lack of it) is the main reason for failure so a rolling programme of re-seeding will disadvantage the areas sown in mid summer.
4, pest damage can be a problem ( eg leather jackets)
5, don't sow too late in the year where frost damage to seedlings is likely to take place.
6, have you considered using a turf system which would allow the grass to be established elsewhere (I realise cost might be an issue).