I'd suggest one specimen rose, or a couple of mini roses. While it is possible to grow four hybrid tea roses in a 4x4 space in a cold climate--I find that they usually outgrow that space in Connecticut, where the growing season is only 6 months. HTs tend to grow straight up, which allows them to be packed tighter into spaces--assuming you don't have issues with fungal diseases--which really take off if they get wet and don't have much airflow from being packed so close together. Florabundas spread out more than HTs--but how much depends on the variety.

You mentioned that the soil had a fungus in it. What kind of soils is beneath it? Does the area have good drainage?
Before you replant find out or you will have the same problems. Soil in a good area doesn't get fungus in it!

ALL soil that isn't sterilized has many different types of fungi in it. What type of fungus?

I agree with Zac, 4x4 is room for one rose. Use soil from your garden, not something from a bag from the store.

In your warm zone and long growing season roses will get much larger than they would for me so I'd stick with one beautiful specimen plant. If it's workable a one of those gorgeous fountaining OGRs would be a real focal point.

What I might do with that space is plant two Munstead Woods (Austin) in opposite quadrangles and then the low frilly white hardy garden geranium (perennial) in the other two opposing quadrangles. Should be quite dramatic--dark red/purple rose and airy white perennial.

Or for a specimen, I might plant one Bourbon--either Souvenir de la Malmaison or its nearly identical twin Mystic Beauty (available from Roses Unlimited). Perhaps for the first year or two, plant some interesting smaller/low-growing annuals in each of the corners.

Or another specimen choice--taller and more upright growing--try Austin's Lady of Shalott--or browse the Austin site for another taller growing, disease-resistant, floriferous shrub with blooms of a different color. Many of his introductions the past couple years would be excellent choices.

Check the Austin cite here:
David Austin site

Are you familiar with helpmefind.com ? Wonderful data base with lots of photos on just about any rose in existence. Look up other roses there.

You would probably need to buy any of these from an online nursery since they are not readily available in local garden centers.

Good luck. I like the idea of your raised bed there.

Kate