At this point, don't stop making marines out of that 1 barracks.
18 Command Center at Natural
20 Take both Refineries in your main base
25 Factory, Reactor on Barracks
30 Tech Lab on Factory, Starport, take 1 Refinery at your Natural
As you're making marines, keep filling up bunkers and build your supply depots in front of those bunkers. You can stop when you have 3 bunkers.
45 Swap Starport and Factory, Start a Banshee and research cloak, add another tech lab to your Factory and research Siege Mode as well as start making Tanks.
At this point you should have:
1 Starport with a tech lab
1 Factory with a tech lab
1 Barracks with a reactor
3 Bunkers full of marines
~3-4 tanks with siege mode
~1-2 Banshees with cloak
This means you can start getting your third base and add 3 more Factories, as well as an armory. You're pretty safe from attacks for now, so just focus on macro.
What I would do is build a raven for defense, and harass a bit with the banshees - try not to lose them, play it safe.
Lift off your barracks from the reactor as well because you don't need any more marines. Just build one of the 3 factories you're about to build on the reactor and start making hellions. Research Blue Flame and start getting attack upgrades for your mech units, ignore armor upgrades until you're at 3/0.
4 Factories is pretty decent for building up a mech army on 3 bases, you shouldn't need more than 5 Thors. When you get 4-5, start building a lot of tanks because the splash damage from tanks is insane in high numbers. Protoss players aren't used to avoiding tank lines so it works out.
When you're thinking of taking a 4th base you can add maybe 3-4 more factories or 2 factories and 2 starports.
What you want to end up with is about 10-12 Tanks, 10 or so Hellions, 5 Thors, around 6 Banshees, 2 Ravens, the marines you built earlier (12 or so), 1 or 2 Vikings, and 5-6 ghosts strictly for EMP/Snipe.
Engagements using this army:
Siege Mode, the toss will walk into you anyways so it works great.
Pull your ghosts off to the side a bit, make sure they're in range to EMP units getting close to your army - but watch for things like High Templars, snipe them as soon as you see them. Just keep scanning the guy's army so you know where all his units are and what his approach will look like.
If you have the ravens/banshees/vikings towards the front of your army you'll immediately kill off any observers and all your cloaked units will do a good amount of damage while your thors absorb a heck of a lot of damage.
Mech will pretty much just melt any Protoss ground army, the only thing that can beat you is early pressure. There isn't a good chance you'll lose a fight when you're maxed out.
Also a good thing to note is when you're maxed out make sure you build more production buildings and mass orbitals so you can sacrifice scvs or use them in your army to repair.