Hi John,
I did in the past use the online coverage calculator by Roger Coude - VE2DBE :-
https://www.ve2dbe.com/english1.html
The results were quite close to the sort of coverage I was getting with my homebrew VHF/UHF antennas but not entirely accurate. Pretty useless with propagation effects though being a line-of-sight/ground-wave coverage type of calculations.
I think the reason radio still fascinates me is that Mother Nature can be a fickle cow and you won't really know how an antenna performs until you actually build it and put it on air. Even then you'll never be 100% sure with changing conditions.
My own piece of lawnmower lead strung around my loft still surprises me with contacts on HF around the world despite protestations from more 'experienced' Hams of "No! No! No!"
Even my first UHF beam was built by trial and error rather than calculations moving around and trimming elements until my field strength meter and VSWR looked good enough. Certainly works and although probably not an 'efficient' way of doings things I definitely had a lot of fun with it!
(Get yourself a NanoVNA if you can, damn handy bit of kit for such stuff finding mine invaluable after being graciously donated by a fellow Charlie Tango member!)
Enjoy yourself with any antenna constructions you undertake as it is all interesting stuff.
It doesn't have to be all expensive or 'exotic' materials either, I've utilised old mains leads, steel washing lines, garden parasol rods and any other junk I can get my hands on for a bit of experimentation!
All the best,
Victor