I would say it's all pretty walk-able really - and I don't really like walking either. I went for a few days earlier in the year. Didn't bother with the maps on the phone - just got a paper map from our hotel reception. Most places seem to do the same map, which in most places are free. They have loads of the main sights marked on and all the street names, and so was pretty easy to get anywhere. The metro there is also pretty easy to use if you'd rather go to the other side of town fairly quickly. Regarding going on roofs to get a great view of the area, which I'm sure is great - but I'd definitely recommend going up the road that runs from Piazza del Popolo to the rear of the Spanish steps. You can see everything practically from up there (and it's obviously free) - it also has a little van at the top that you can purchase a cold beer from to refresh yourself whilst taking in the sights. Have a look for yourself:
https://www.google.co.uk/maps/place/Spanish+Steps/@41.9096463,12.4801246,3a,75y,220.31h,92t/data=!3m7!1e1!3m5!1s1t-CeNuI1BMUtn6Jd2QWQg!2e0!6s%2F%2Fgeo3.ggpht.com%2Fcbk%3Fpanoid%3D1t-CeNuI1BMUtn6Jd2QWQg%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D100%26h%3D80%26yaw%3D333.6066%26pitch%3D0!7i13312!8i6656!4m2!3m1!1s0x132f60541678ae75:0x7fc0d4978aae690f!6m1!1e1