This is the best use for a garage repeater I can come up with.
Edited to add: If you're trying to get __into__ a repeater, another option is a cross-band repeater that transmits on the repeater input channel. Were it me, I'd use Motorola's DTR and DLR 900 MHz radios for the handheld terminals, since they can be set up with enough encryption to keep noobs and jammers out of your transmitter. 900 MHz digital is described to have excellent building penetration characteristics, so it should be able to find a path to your outdoor transmitter package without much trouble.
If you're not trying to get into someone else's repeater but just want to get outside your house with enough power to get reception, you might consider the Retevis RT97. It's a five-watt "lunchbox" repeater that can be set up outside; all you need is enough power to make it through / around the cinderblock to transmit successfully, however you're going to be relying on your handheld and its indoor antenna for all the reception involved, which is unfortunate.
The DTR and DLR radios are (mostly) cross-compatible, albeit with some new features only existing in the DLR1020 and DLR1060. However, the older DTR410 and DTR550 have removable antennas, which might be better suited to building a cross-band repeater.
Were it me, I'd use a DTR550 in the repeater box, and a DLR1020 as a wireless speaker-mic to access the rooftop radio in your situation. Alternately, you could consider the (discontinued) DTR410 on eBay, as it may (frequently) be cheaper than a new DLR1020 in spite of greater capabilities in a lot of ways.
Yes, I have similar problems with running coax where I live.