I am not a huge fan of pistol caliber carbines but I can see the utility of a carbine that takes the same magazines as your handgun in certain situations. Double Diamond Law Enforcement Supply (DDLES) makes AR-15 lowers that accept GLOCK magazines.
The lowers are available for either the GLOCK small frame magazines (9mm, .40SW, etc) or large frame magazines (.45ACP, 10MM). They are also available with a number of options like your choice of 6065 or 7075 aluminum, various selector markings, and custom engraving (handy for those building SBRs). They also sell barrels and complete uppers in various calibers to complete your build.
If I was inclined to build a pistol caliber carbine, it would be on one of these lowers. Check out the DDLES AR-15 GLOCK Magazine Lowers on DoubleDiamondSupply.com.