Hello Ashleigh
I have been converting some pasture to a raised bed system over the last year or so having also been inspired by Charles to try no-dig. Having decided not to cover with a thick manure layer due to the large quantity needed and the good fertility of the soil, I tried a some different ways to kill the grass and weeds.
– Mypex woven ground cover fabric. This killed the grasses and weeds in about 6 months or so and can be re-used many times to gradually clear a large area. It is worth getting a good quality fabric to exclude as much light as possible. (about 100gsm). Try allplas.co.uk for large rolls.
– Silage clamp sheeting. This can be a cheaper option if you can pick up an old roll from an agricultural merchant at a discount. It is very effective but may encourage slugs although i have not found this a problem
– Straw. I got some large bales of pea straw which were available locally and laid slices about 6 inches thick over the ground. They expanded when wet and killed all grass and weeds. I found using straw this way expensive although you are adding fertility as the straw rots. There was also some residue which could be left on the ground or composted. Might be worth thinking about if you can pick up some spoiled straw cheaply.
Before covering I cut the grass short and spread a thin layer of manure as recommended by Charles in his books. A few tough perennial weeds did survive but can be easily removed. I found about 6 months is needed to kill most plants but there is a trade off between how fast you want the ground ready and how many weeds and tough grasses are left.
Good luck! Andy