StarCraft2: how can Terran wall-in if choke exit is on the right bottom side?

Solution 1:

As you are going for Technology, you might want to consider to place a Bunker after you lift your Rax.

Scouting is key to determine if it's necessary to spent effort on getting a tight wall...

Solution 2:

Generally players will create a tight wall off with there naked barracks (no add-ons) and once they are ready to build a tech lab or reactor they will lift off the barracks and land it with enough space (add-on facing the ramp).

While this is more vulnerable then other spawn positions where your add-on is on the other side of the barracks, it still provides you with a tight wall off and is better than nothing.

Specifically in the 1-1-1 build you mentioned. Because there is so much add-on switching going on, it is possible to have either your factory or starport (depending on what units you go) building your extra add-ons. Most players also throw down a second barracks shortly after as well (which can also help build add-ons)

Solution 3:

I often wall in with my first Supply Depot and Barracks at the bottom of the ramp. So long as you place the depot on the correct side, you should always be able to build an add-on without blocking where you'd place a Command Centre at your natural. This will usually prevent a worker from scouting whether you took your gas. Other times their scouting worker will get trapped inside your base, which at least ensures you can kill it. Make sure you're ready to defend the SCV building the Barracks.