Before you start building your raised bed system, you should cultivate the whole section the same way you would for any other vegetable garden design. Remove all weeds, loosen and level the soil, and remove any large rocks or other foreign items.
Ideally, you want to make your beds 4 feet wide so you can reach the center from either side, giving you access to the entire width. Since you’re going to have to walk around the end of the bed to get to the other side, they shouldn’t be too long – probably 10 feet maximum.
Most of the paths between the beds should be 18 inches (or more) wide, with a few 2 to 3 foot paths for wheelbarrow access.
The edging of your bed can be any height, really. It will depend on the soil you’ve got to work with for one thing. If you need to add more organic matter for effective growing, you’ll need higher beds than if the soil is already in good shape.