nuclearcat wroteOutdoor, UV resistant cat5/6/7 exist too.
"Black" wire means nothing, it stupid advice, sorry. Especially stupid is about "some interference". Interference resistance is dependent on shielding and cable pair twisting. As said before - using shield is not easy thing, even with grounding ,there is many details, so you can avoid it, but as DSL signal is not Khz, but still below 10Mhz, any twisted pair(even cat3) with proper wire gauge and material (should be pure copper) is suitable. using regular, non-twisted cable is not recommended.
P.S. About plastic coating thick enough to resude interference - it shows person is completely illiterate in properties of electrical signalling, and he dont even know how things work.
About outdoor resistance, everything depends on insulation, or cable jacket material - it should be outdoor type and UV resistant. You need to ask cable details, if you care about that, and yes thats one more reason to not run cable outside building (UV resistance limits cable choice a lot). But technically your cable may survive year or two outside.
Outdoor, uv resistant in any case will be much more expensive than normal cable with proper insulation.
Hmm to tell you the truth I was not very convinced that copper wires (no matter how thick they were especially that they are not twisted) would be better than cat5/6/7. That's why I asked since you seem more knowledgeable in this field than I am (I read your article). So thank you for clarifying.
I have another question, if I may ask:
Supposing you could get any of the cables from the list below (and supposing money was not an issue), what would you choose and why?
If it is case dependent and you cannot give a general answer, I can email you a pdf file showing the wiring in my building (it might be of help to you with your article about bad wiring).
Thank you in advance.