I just finished 23m2 of indian Sandstone behind my 3 bed semi. it has amazing colours that change when wet/dry . Also contains fossils which i find facinating. There are amazing deals on stone at the moment. i rang around got the best price i could and then bargained more discount for cash on the day of purchase. Worked out at €15 m2. Paved up to the back door. Materials hardcore/Sand/cement. €388. 3.5 Days to finish (with help)
Regrading the manhole/ Gullies. Simply make a timber box with no bottom or top. Place over the required access point, backfill around with gravel/ sand cement and then cut a stone to sit on top. works a treat and no messing with the drainage.
hope this helps