A judge would be looking for all roses to be grown to their best. Roses put in layers need their stems cut...dont cut So, arrange your diplay (if the schedule states ) in an allround shape
If not quoted on schedule arrange to make a pleasing display with your best in the front to catch the judges eye!Use the deepest bowl you can find, nothing to detract from the judges eye, and use foam to keep stems in place.
Good luck may you be a first prize winner

Here is a link that might be useful: Garden Web

You might find the link explains what a bowl of roses looks like in the UK

Here is a link that might be useful: A bowl of HTs

No picture of the bowl. Is this "bowl" for an ARS Class? The only "bowl" for an ARS show is a single bloom floating in a bowl.