For shopping, Qatar is not the cheapest place, I mean if you have a stop-over in Dubai, you're better off purchasing from there.

In case you wanna shop, on Al Sadd, you have Centerpoint (Al Asmakh) mall, where you got e-Max, an electronics store. You have also NASR street, where many small electronics shops exist.

You can grab a cab to city center (20-30 mins) and go to carrefor for the best prices in town.

Cheers!