See if neighbours are able to receive with indoor aerials, is how I'd start, as that at least proves it can be done. If someone has chosen to use an outside aerial after exhausting their indoor options it starts to get more costly.
Do also remember (if you have rooms with a TV aerial feed) that a cheap 15 to 20 quid Freeview box wired into a music centre or some other type of amp would give you the full range of BBC national radio stations, and possibly in better quality than on DAB.
Similarly multi-room satellite is easy enough (an LNB [piece at the end of the arm] can have up to to 8 cables, so could feed up to 8 rooms, and ways exist to go up to 24 outputs) so with FreeSat a wide range of TV and radio could be fed to rooms indoors. The lowest cost FreeSat boxes are under 75 pounds I think, so could be cheaper than a number of DAB radios anyway !
Using these alternatives blocks listening of 'local' stations (both BBC and commercial) to an extent, compared with DAB, but can give other choices not so widely available on DAB.
Sorry if that's a bit too far off your DAB question, but for people who search for DAB and then find there is poor/no reception if they are shielded by mountains or hills, Freeview and [more likely] satellite are options which can provide greater choice and won't really be 'optional' over time, with the big digital TV switchover taking place over the next 30-ish months.
Of course many people would think twice about using a Freeview box in their kitchen, if it's anything like as small as mine (!) but if someone is keen on 6 Music, Radio 7, FiveLive, or 1 Xtra, for example, then it may work better than DAB and a cheap micro/midi system with speakers could be put on top of wall cupboards, perhaps (thinking back to the cupboards we had when I was a child, perhaps more awkward these days if fitted right to the ceiling).