Anything composted is going to help.

I would dig everything in, water well, water again, wait for weeds to come up, and pull them before putting the roses in. Then after you plant, mulch heavily to discourage any further weed growth. Much easier to de-weed thoroughly FIRST before the new plants go in.

Ah, a blank canvas.
Here's an idea:
If you have a lawn, spread the clippings on the area (unless it is a bermuda grass lawn). Mow up any dry leaves you have and spread them too. In other words, make the area into one big compost heap. Since you want to plant roses, you may wish to wait until early spring to plant anyway. Make sure to visit the Rose Forum to find out which roses will perform best in your area.

We used the compost method two years ago on a gravel driveway. After removing the gravel, the plastic, and as much of the 40 years of oil and grease as possible, we loaded it with all of our grass and leaves for about five months, watered, and turned it all over. It is not the best soil, but it is now workable.

Sounds like you have your work cut out for you. Let me start off by saying "you will always have weeds" so why wait to plant until you pull them. Sounds silly.

When starting a new garden you can do one of two things, you can amend the entire area or just dig the holes for each plant and amend the hole. Much cheaper

Plant roses with 1 cup of superphosphate & 1/2 cup sulfate of potash and 1 TB spoon per plant of Sulfate of ammonia (21-0-0). You mentioned these roses were in pots. I don't believe you will have to worry about using to much of anything, since they are in their own soil. Put at least 4 to 6 inches of mulch.

I am going to write you more by e-mail. Good luck Debbie

If you have access to some good stable manure, that could be really good as an addition. I found some when I lived in Manhattan Beach (we had to fill in an area that was almost 4' deep when we added retaining walls), and then I added in lots of bone meal and blood meal, as well as Dr. Earth stuff. You wouldn't believe the size of the sweet peas I grew that year, flower stems were well over a foot long with at least 6 flowers on each stem (and huge flowers, too!), I had ranunculus with flowers the size of roses.

The thing with stable manure, is make sure it's either been composted to eliminate weed seeds, or the horses were not grass fed since their digestive system does not kill seeds.

--Ron

I'm glad to see that Beberose is going to help you. She is a Rosarian who lives and gardens in San Diego.... so who would know better how to help you. Good luck.