[scezy]

Hi i'm going to be building a raised bed for my mother,out of scaffold boards.It is going to be 13 feet longx4feet wide,and two boards high.It is going to be situated on a slightly sloping concrete drive.Can anyone give me any advice on what i need to do(handy tips)I was worried about the mud washing away out the bottom,also i think he is going to use topsoil,what do you think?
Regards  Scezy

[Stree]

First the slope.  This will be handy for drainage, so not a bad thing. If its sat 4" lower at one end than the other then a few bricks should level it up on top.
This will also leave a tapered gap from the end on  the floor to the end on  the bricks/ timber/ whatever you use.
To stop soil washing out of this I would fix 1/2" galv wire mesh to the inside of the beds at the bottom about 18" of which should  lay on the floor... The weight of the soil will keep it there.
Then, some  weed membrane, two layers if its cheap stuff, this will physically stop the soil spilling out but let water drain....... If it was me I would add 20mm gravel directly on the membrane then soil,  the gravel so the soil at the bottom didn't get waterlogged and sour, plus it  will be better fot overall drainage and aeration.
You could use some 4 foot lengths of board and section the bed into divisions and try different methods and soils, drainage etc in each.