I build raised bed gardens. If you have access to building supplies you can do this cheaper. I order 18 2x4's from the building supply store, and I ask if 6 of them can be cut in half. They usually don't charge me to cut them, and since I don't demand a certain delivery time, they don't charge me for delivery. I could wait a few days for delivery, however. I get 8' lengths, but the size isn't really important. I also order about a pound or pound and a half of nails. I make a 4'x8' box. It slaps together in about 2 hours with me alone working on it. If I had help it would take a lot less time. It will be aproximately 20" high. I put what ever in the bottom. Sometimes I put lawn rakings and broken branches in the bottom. The last one I built I put blocks of wood in that I knew DH would never get around to chopping. You could put in rocks or what have you. The reason I do this is because vegetables don't usually grow any deeper than 8"to 10" deep. I top it up with dirt. Sometimes I beg dirt from the neighbors, or I take some from my yard. You may have to but a few cubic yards of dirt from a landscaping place, but I havn't needed to do that yet. The first one I built, I put it 2' from the wall so I could reach over it to weed and harvest, but I have since found that isn't necessary for me. I can stretch over the 4' to reach my veggies, but if you are arthritic, you may want to have it built so it is accessable from both sides.
For planting, I just simply broadcast my seeds, and cover with dirt. I don't need to make rows, because I will never rotatill this garden. I use practically every inch of space. These gardens don't get weeds, because the weeds don't grow up from the ground through 14" of rock, wood, or even dirt. Any weeds I get are from airborn seeds. Since they haven't established a strong root system when I discover them they just take a second to pull. I doubt if I spend a total of 30 minutes combined all year weeding the garden. As I walk by, I might notice a weed starting to grow so I pull it. I don't even have to bend over to do it. Sometimes I just sit on the edge and search through the veggies for weeds, but as I say, there are very very few weeds. I have heard these type of gardens require a lot of water, but that has not been the case with me. I built them up against the back of the garage to get the heat from the bricks in the evenings, and the water runs off the roof when in rains and waters the garden. Perhaps 2 or 3 times a season I will water with the hose when I wash the car, but that is about it. You will have to take into consideration your own weather and gardening conditions.
The yield is phenomanal. I don't have to worry about animals getting into it since it is right by the house. Space isn't wasted on rows. Over the years I have had success with potatoes, green beans, yellow beans, radishes, carrots, beets, turnips, and spinach. I have three gardens and hope to build another one this spring. I started this about 10 years ago, and the garden boxes have held up well. Last summer they kept the wolf away from the door when money was tight, and I suppose they will do the same this year.
For planting, I just simply broadcast my seeds, and cover with dirt. I don't need to make rows, because I will never rotatill this garden. I use practically every inch of space. These gardens don't get weeds, because the weeds don't grow up from the ground through 14" of rock, wood, or even dirt. Any weeds I get are from airborn seeds. Since they haven't established a strong root system when I discover them they just take a second to pull. I doubt if I spend a total of 30 minutes combined all year weeding the garden. As I walk by, I might notice a weed starting to grow so I pull it. I don't even have to bend over to do it. Sometimes I just sit on the edge and search through the veggies for weeds, but as I say, there are very very few weeds. I have heard these type of gardens require a lot of water, but that has not been the case with me. I built them up against the back of the garage to get the heat from the bricks in the evenings, and the water runs off the roof when in rains and waters the garden. Perhaps 2 or 3 times a season I will water with the hose when I wash the car, but that is about it. You will have to take into consideration your own weather and gardening conditions.
The yield is phenomanal. I don't have to worry about animals getting into it since it is right by the house. Space isn't wasted on rows. Over the years I have had success with potatoes, green beans, yellow beans, radishes, carrots, beets, turnips, and spinach. I have three gardens and hope to build another one this spring. I started this about 10 years ago, and the garden boxes have held up well. Last summer they kept the wolf away from the door when money was tight, and I suppose they will do the same this year.
I am going to share your idea with my DH and see what he thinks. I have limited mobility and am far passed being able to tend to my "real" gardens any longer... your idea is great! 
tomatoes and will pick them himself (Riddler used to raid our real garden all the time 
) DH puts the buckets of tomatoes up on the picnic table when they are ripe and Riddler is running around... or else we would have none left! 
I build it 6 2x4's high, but since the 2x4's are not true it only totals about 20"-22" high.
