Makes no difference whether CAT 5 is run inside or outside. I recently done a run of CAT 5 from me mate's house to a garage at the bottom of his garden that he converted into a recording studio, about twenty metres total run, it worked flawlessly.
I'd agree with above, one repeater, installed midway. Bear in mind the repeater will need a power supply, so nearby mains is essential.
You could run a twin core cable to take a DC low voltage power supply with the CAT 5 to the repeater but DC voltage is likely to drop a little over 100 metres, that one's very much a 'suck it and see' situation.
I have run 12 and 24 volt cable runs to CCTV cameras over about 80 metres before and it's worked ok.