Doing some quick calculations
I have a feeling you're gonna be
seriously over crowded unless
all your roses are 18"x18" midgets.

To give you an idea I just finished planting
my 1m x 10m bed with 6 roses. Min 5' center
to center.

Overcrowding causes disease & maintenance
problems. There is a case for squeezing together
tough colorful roses that you want to make a nice
stand with. but they must be tough and disease
resistant and must have a nice habit. I have planted
4 x 2m bush roses in a 3m bed and they are growing
together nicely but I carefully selected them for this purpose.

I think it depends on the type of roses you choose. For instance,
because of its upright nature, Edmunds recommended that I plant my 3
Belamis about 1 1/2 ft center to center. That allows for its normal 3
ft. spread. It should create a nice "single" bush with about a 5 - 6
foot diameter. Of course, alternately, I could have planted them
further apart and kept the plants distinctive, but I didn't really
want that American Beautyesque (the film, not the rose) row of HT
soldiers. I wanted more the effect that my big Aloha has - I think
that someone planted three separate bushes in a triangle years and
years ago and now, it just looks like one BIG plant.

Yes. Stands like that are useful though
I get bugged by Austin who recommends
it for all his roses. It speaks of a certain
weakness in the cultivar.

I wouldn't recommend it for different
types of rose though. As it is my Pink
Gruss An Aachen is getting overgrown
by the Pilgrim 4' away.

--
Theo in Zone 5
Kansas City