raised-bed Filling a raised bed

Hey guys. I'm filling a raised bed with about 5 yards of material. I've got a nice big pile of old dry grass clippings to mix into the bottom layers. What percent of compost should I mix into the soil? I understand you shouldn't grow veggies in pure compost. (I know they can grow in pure but a mixture or tip dressing is better?)

Should I buy 4 yards of garden soil and a yard of compost mixed into the top? I'll probably add some leaves and straw and stuff as the year goes by.
I should specify this is for normal veggies. Starting with standard suburban clay and buying topsoil/compost.
Filling it with compost is fine, add in up to a 3rd crushed lava rock for aeration and minerals
Mulching is a great idea