The first time I was asked to build a raised garden bed was for the mother of a friend of mine who was confined to a wheelchair after a hip injury. She missed her garden and we built a couple of raised flower beds for her.
They were such a success that we spent the next spring building multiple raised beds for her and eventually transformed her entire garden to raised beds and packed paths that she could access easily with wheelchair or garden scooter.
After those first experiments I’ve created many raised garden beds for myself and others. The materials I use change with what is available, but the size and structure remain pretty much the same.
What goes into the raised bed is more important than what you use to build it. Without good soil there’s no point. I use a method that I like to start in the fall for next season’s planting. First cover the bottom of the raised bed with several thicknesses of newspaper, about an inch. Use newsprint, not the slick ads. This will act as a barrier as well as killing the grass and other weeds and will eventually break down into compost.
From here on out we are basically going to be building a compost pile. Start with a layer of yard clippings, next some soil and/or manure if you have access to it, then add a layer of peat moss. As you build a raised garden bed keep layering the soil and compost to be, heaping them until you are quite a bit above the height of the bed sprinkling each layer with water as you go. Let the raised garden bed sit over the winter. It will decay and settle to give you the perfect spot to start your spring peas.