I keep viewing the various issues that pop up around weeds, roses and other perennials, in this thread and others. I haven't tried the cardboard plus mulch. After giving quite a lot of thought ( because any major project implies major work) I arrived to the decision make it work. So I will stick to the carboard plus mulch method.
1.Roses can withstand thick mulching because their living parts are quite above the light black out layer.
2. Other shrubby/bushy perennials the same
3. Herbaceous perennials. I suspect that for most they will have to be lifted potted and kept apart until the full bed is free of the obnoxious weeds ( in my case quack grass , others bermuda grass and so on). In general these weeds are mainly worrisome because they store energy in underground rhyzomes that allows them to keep living for lengthy periods of time in a latent situation. But if one can keep the darkness going on for ever then all unwanted weeds will eventually dissappear. It is just a question of patience only. Yes the underside of the roses will be permanently some type of mulch instead of visible soil. I personally don't care if I see bare ground or mulch. I definitely prefer no weeds.
4. Once a year at least the layout may need to be removed to add manure and incorporate the rotten mulch into the soil.
5. Since I haven't tried it at all , I really don't know how often does the bed require the dark cardboard , once it has efectively removed these really noxious weeds.
Those weeds growing just under the roses, can be smothered too with this same method. Instead of cardboard stuffing thickly shredded newspaper/ brown bag paper (really thick so that even a single blade intending to grow out from it has not chance to get anylight.). (see also @AquaEyes
says just near above: <lay down cardboard in the spaces between the roses, and use newspaper around the roses>
7. Once the bed has been freed of weeds, then companion plants can be placed back again making sure that their roots balls do not contain any unwanted rhyzomes( my quack grass roots are very easy to distinguish). These companion perennials can be placed in holes carved into the cardboard layout.
Summing up, @mustbnuts
I really want to thank you for pointing out this method.
It is lengthy, but very logically consistent and if once understood the underlying principles, one can become imaginative and continue improving it with added details.
PS needless to add but always a good reminder, its absolutely environmentally friendly