You can use leaves but should use oak leaves or some other type that doesn't mat down. Maple leaves are notorious for doing that. They mat so bad at times no oxygen gets to them and they smell badly when disturbed. Oak leaves don't mat. Shredded leaves look bwtter in my opinion. Leaves will decompose on site quickly so don't plan on an application lasting a full season. For that reason bark or wood chips are better. I use only shredded oak leaves as winter protection, then pull them back from the bushes in spring and leave them in the beds. By mid summer, they've all but disappeared.

I think we have elm and cottonwood trees.

How large is your rose bed?

The top part of our backyard is 26ft long X 6 ft wide.
The side is 45ft long x 5ft wide.
I purchase shredded hardwood mulch in bulk.
Total cost about $65 to do those areas I listed above at a depth of 3" deep.
Lasts all season here.

Some cities/towns offer free wood chips. Maybe check into that.

Karl covered about using leaves and what to expect. So, not much to say about leaves.

According to this article Cottonwood leaves should not be used for mulch.
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If you have a cottonwood tree, chances are good that you've experienced difficulty in growing things under your tree. This is because cottonwood leaves are slightly alkaline in nature, and can raise the pH of the soil to the point that plants have trouble growing in it. The problem can spread if you use cottonwood leaves for mulch. The solution is to compost your leaves. Finished compost has a neutral pH regardless of the pH of the plants used. Once your leaves have been turned into compost, you can amend it into soil or use it as mulch.

Click below to read full article:

Here is a link that might be useful: cottowood article

Thanks so much for all the info. Guess I will not be using those leaves for mulching the roses. I was just hoping to be able to save some money and put them to some use.

rehabbingisgreen,
The article I provided above carries a warning at the end of it about even composting cottonwood leaves.
Says this, in case you missed it.
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"Tips & Warnings
According to to the University of Colorado, the tannin in cottonwood leaves can affect the pH of compost if used in high quantities. When composting cottonwood leaves, dilute the tannin in the compost pile by making cottonwood leaves only a small part of your compost pile."