Well, on my last visit to Brum in Dec 2012, what a disappointment!
I went round all the shops I used to go to when I lived there between 2003 and 2007 and did not find a single record worth buying. They all had multiple copies of some regular (not to say "crap") tunes by Dekker, Biggs and Pluto, but that was it really.
Roots reggae records you can forget about it. I wonder if this has all been skimmed by UK ebay sellers, or I suppose those records don't even make it to the second hand shops, they just get bought by sellers from the owners direct though local newspapers "records wanted" ads. I wonder what are your thought on this. Where are the bloody records gone?
There used to be a fair bit of goods 80's or digital reggae around in shops like The Diskery or Music & Video Exchange, but it seems that it's all gone too now, and that only remains some forgettable 90's/2000s dancehall.
About Summit, Lats time I went there it was on stephenson street by New street station, and it was all dancehall, especially dvds and a few rythm series, but most of the business seemed to be the barber shop. don't know if that's still the case now
You can always try the Diskery (by Chinatown/bullring area), MVE, Swordfish (for LPs),the indoor bullring market.. but don't get too excited, you might end up disappointed.