The size of the bloom, not the size of the plant. Minis (and mini-floras, which usually have larger blooms than minis) can range in size from micro-minis (small in plant size and bloom size, usually under 2' tall) to 3' - 5' tall. Mini climbers can get to 10' tall.

So, you should ask about the growth habit of the variety, like the "big ones" it varies widely.

If you want true miniature roses, get some micro mini roses.
They are tiny, both bush size and bloom size. I dought you would find them locally, so google micro mini roses.