Hello Al
The two maps I mainly used were OL188 Builth Wells/Llanfair-ym-Muallt and OL200 Llandidrod Wells & Elan Valley.
The walks weren't in a guide book or on a website and, mainly, they were very short - except the one on Drygarn Fawr, which was the only one which might have difficult navigation in poor weather. This one started at the head of Caban coch reservoir and has a fair amount of fairly featureless moorland and plenty of opportunity for not finishing up where you might have planned to finish up (!)
The other walks were very short - eg the Garth trip is straight out from Builth Wells and is a pleasant hour or so stroll on a green hill with cracking views. Similarly, the Begwns/Roundabout walk is a pussycat done from the minor road just South of Painscastle - lots of opportunities for even further hazard-free explorations on this friendly hill (see? I'm encouraging you to have a walk on this one!)
The Carneddau is just East of BW and is a bit more like hillwalking, but is pretty easy - the main problem seems to be finding parking on the main road, - but a lay by on the A481 near Lower Pentre seems as good a place as anywhere to park (although it was officially closed when I went there). From the map, there seems to be more opportunities to walk on the nearby Castle Bank hill just a bit North-East from Carneddau to make a fuller expedition of this hill. Good hill, though - no difficulties with it...
The Gwaunceste Hill walk was a quick bag from Three Wells near Gascwm. This is mainly heather moorland with tracks and bridleways. Nothing specially difficult about the area, although I found the overal geography of how the area fits together a bit difficult to understand..
In general terms, the hills around BW are relatively small and isolated or in small groups - such that the opportunities for getting properly lost are restricted and there's nothing much to fall off. I dare say there'll be guidebooks available in the local shops which will have somewhat better routes than my quick and dirty bagging walks...
I'm not much of an authority on the area, though as I've only been the once.....