Just get out there and wander, Rome may not be heaven for a stylish chap but its only a few steps from the Pearly Gates themselves. If you are only after brands then Via Condotti and close by will suit you fine, or wander up past Spanish Steps and beyond to visit Brioni, I called in last month which was a mistake as i was wearing Brioni and they swooped thinking i had money to spend.... Or go there, talk big and try everything on, be treated like a gent
I Picked up a few jackets on the main street that leads off from Piazza Republica, beautiful cloth, cut and color (Sports jackets) and both for 300 euros! (thats both for 300, not 300 each)I only wanted one but my better half sniffed a bargain and pushed the deal. There are a lot of these small tailors where you can find beautiful kit, I know tailoring and quality and these bargains were there to be had, also picked up a short raincoat for a third of the price on Piazza Repubilca itself.
If i was to offer a slight criticism then i think near every shop wanted to push Zegna, I am guessing because they assumed i was a tourist and would be impressed by Zegna, (that being said, they were at 600 euros rather than advertised 1200 so i was slightly impressed). Fair enough they are there to push sales but as soon as i started to chat (in Italian) and talked of the cloth, cut, etc they were all happy, friendly and started pulling out lots of other gear. I didn't go to buy clothes but in Rome its too easy to look and shop when you wander streets, enjoying the sights, eating slices of pizza and drinking coffee etc. I would avoid the out of town malls and discount malls because why go to Rome and not discover for yourself, you won't be disappointed.
A few years back i lived in Rome for a while, grand days, so i know it well but you will be fine if you stick to the main center/tourist areas and simply follow your nose. Buy some gloves near the Spanish steps, follow Audrey Hepburn and try not to look like a tourist, you will love it I'm sure.
if I can help with any more specific information then ask and i will if i can....
DLQ