<font color="blue"> I used a rear blade swiveld and tilted to the max. This cut a deep ditch in no time. It is nicly sloped and now planted to grass </font>
I've recut some of my ditch, never done it from scratch, but I followed this same method. Angle the blade & tilt it, let the cutting edge engage the ground so that the corner of the blade makes the cut. I will say that the ditch work I did was started with an inexpensive swivel only blade and having to work in the ditch is what inspired me to switch to a much beefier tilt/swivel/offset blade from Corriher. Having the right blade made the job go much easier.
If the ditch is basically a dry ditch and only is wet during/after a rain, it should be tapered enough that you can grow grass on it and mow through it so once it is done, you shouldn't really have to maintain it other than mowing.