troubleinstore muttered:

Question is after the grass has been cutt, do I have to kill all the grass
and weeds (I've got a tub of sodium clorate) and then level the ground or
will the sheer volume of pebble on top of the membrane do this for me.

Sodium chlorate would not be suitable anyway as it reduces your options for
any future planting in the soil, glyphosate would be a better idea... but
even so it would be a heavy job and might need several applications.

One way would be to tackle it bit by bit starting with the area furthest
away from your access point (for any machinery you might need to hire) so
you don't trash anything that's finished.

Or how about a compromise by gravelling the major part and putting in some
raised beds using sleepers? I think you'd have to get _some_ help at some
point though.