Those stacking blocks are easy to work with and not too expensive. Wood is cheaper but can rot quickly. The key thing is to make sure the first course of blocks are perfectly level. A raised bed would hide the base of your deck and make it appear more "rooted" (if you'll excuse the expression) to the surrounding landscape.

Be forewarned, however, that those tree roots might start moving up into the raised bed, hungry for all the water and nutrients you give to the roses. Digging out as much of them as you can might slow them down.

I've found tree roots 40' away from the tree that sent them out.

Keep in mind a tree's canopy has a similar amount of roots to support it. Many trees grow their roots down far enough below the surface to allow other plants to be planted at their base. The only problem is when fertilizing and watering those plantings, you're also doing the same to the tree. Likewise, if you fertilize and water your lawn well, a nearby tree will grow roots towards and into your lawn. Like roses, the tree's feeder roots are close to the soil surface and they can create quite a network of intertwined roots.
Like hoovb stated they can grow quite a distance. A big tree requires large strong anchor roots to keep it from toppling down in high winds and when the soil becomes saturated.
As stated above, a raised bed would solve the problem for a while and would hide the base of your deck. Eventually you may have to plant your roses in very large containers to keep tree roots from interfering with the bushes. To keep wandering tree roots out of the containers and rose roots from growing out of them, lifting the container and turning it in the hole occassionally will serve that purpose. A raised bed would serve to hide the containers so the bushes would appear to be in the ground.
Really large containers!

Thank you so much HoovB and Karl! Those nasty tree roots look like I've got some major sawing to do!!! I am quite horrified by the mess I've got on my hands. I used to love trees and should be ashamed of wishing I had less! They throw roots out the wazoo and unwanted shade in the autumn, but I can't bear to think of cutting them down.

Karl, with a really giant pot though, it means that I have to have a very high raised bed too, right? Also if that raised bed is going to be so high, does this mean I need to kill the grass? or will it just die on its own due to it being smothered by all that dirt and mulch.

Many apologies too for my belated thanks for the helpful advice!

Hopefully this doesn't count as stealing but I don't think they'll mind...

http://forums.gardenweb.com/forums/load/rosesgal/msg1012161330772.html?9

Take a closer look at the roddie to the left side of the gate bring your eyes down a bit note that stone border looks good huh ( they also come in square ) add a third layer and work carefully with the root

Side note: it may look a bit pricy and yes it is some added work but that is how one should do it.

You could use the 15 gallon plastic nursery "tree pots", wider than tall. Ask Jeri for a picture, she plants all her roses in those sunk into the ground because of the gophers in her area. Just sink them into the soil of the raised bed, make the raised bed walls just tall enough to hide them.

Plus if you ever wanted to move them--switch out one rose for another, it would be a quick and easy job.

What kind of tree is it? If it is maple, its roots will be aggressive and compete with your roses esp. if you make a raised bed.

KG,

You can also use black corrugated PVC pipe like I did. You can cut it to the desired length and bury it as deep as you want. I used 18" diameter for a row of roses I planted on a fence that had a roof drain running through it. Same solution to a little bit different problem. Not sure what the cost comparison would be to large pots because I horse traded mine from a customer. Necessity is a mutha so you could always solve the barrier at the bottom for intrusion of tree roots in any number of ways. What I like about the pipe is the strength and the fact that it's impervious to the elements. The part of mine that is above grade is wrapped with the color of PVC lawn border that matches your deck.

Place cardboard down before you fill the bed with soil or what ever you're going to use as fill. The cardboard will be a barrier between the grass and the soil in the bed. In a short time the grass will die and disappear. If you're not going to complete the project until next spring place the cardboard down now with a few bricks to hold it. By spring there will be no grass left, just bare ground.
Using the squat pots is a great suggestion. Your raised bed in the area pictured should be plenty tall enough to hide the pots.
Keep in mind you'll want to use own root plants as grafted plants may set up too high to cover the bud union, especially in a squat pot. That's not a problem in California where Jeri lives but could be in your zone 5.
Another thought, don't fill the bed until you've placed the pots. It'll be easier to move them around to get the best look.
You don't have to use soil in the bed with the pots. Fill the spaces between the pots with mulch. As it settles you can top it off to keep it looking good.
This would be a good place to use a drip system for your watering needs. Just run it from pot to pot without watering the mulch in between.
Even with a barrier and a raised bed, the tree roots may be a problem in the future. They're not adverse to growing in mulch or what ever else you may use as fill. Should you decide to use landscape fabric or plastic sheeting as a barrier, the tree roots will grow into it. Attempting to remove plastic or landscape fabric from tree roots can be difficult.
The previous owners of my home used heavy plastic under river rocks all around the house. When I removed the rocks and plastic the shrubbery and evergreen roots were entangled in it making it impossible to remove in some cases.

soooo many thanks to everyone! for all your thoughts and wisdom and greeeeaat ideas-- I am such a lucky girl!

Everyone, no wonder everything in my front yard keeps dying. It is surrounded by 2 beautiful maples and an ornamental plum tree. I've tried other plantings even the "invasive" ones there-bee balm- and they remain so frail and tiny except for my most hated Queen Elizabeth that I'm itching to get rid of. But that is another issue, LOL! so it looks like I have to do something similar as with my deck. Besides, the deck is crucial unlike the front of my house. The deck has the great sunlight and the height that my climbers can climb along.

I am bookmarking this page!!! thank you, everyone!