They'll be fine on both sides if he corrects spoke lines at hub and rim, achieves uniform high tension, and stress relieves. Building robust bicycle wheels including these steps is so simple that school children can do it on their first try as Jobst Brandt proved when he had his sons each build a wheel set using only his book The Bicycle Wheel for instructions. It does take more patience than many school children and some adults have.

Machines usually don't do all these things for cost reasons. Bad wheel builders don't because they'd rather hang out in their workshop, build wheels during the day time, and drink beer at night instead of reading a book.

With a good build and conventional spoke counts any quality spoke with a properly supported elbow will work. Jobst isn't a small guy and has hundreds of thousands of miles on a single set of 1.8/1.6mm spokes. He's also said that 1.5mm spokes would be strong enough but are too much of a hassle to deal with (torsional rigidity increases with the fourth power of diameter, so a 1.8mm spoke is 100% stiffer than a 1.5mm spoke and 1.6mm spoke still 30% better). This is exacerbated by the 2.0mm threads which usually accompany a 1.5mm butted section since the larger thread results in higher torque transmission to the spoke during building with more windup than if a 1.8mm thread was used.

Small (1.8mm) spokes in big (2.5mm to clear the 2.3mm threads on a 2.0mm spoke) holes often fail due to an unsupported bend in the head end with high residual stress that cannot be relieved which leads to spoke breakage until you rebuild with thicker spokes. Long elbows to make life easier for lacing machines can also cause problems unless you take up the slack with head washers.

Bigger and more plentiful spokes mean you might get away with bad builds longer but you're better off just doing things the right way.

Road quality has little to do with it. Spokes fail due to fatigue and it's the 750 cycles per mile that do it not the far less frequent pot holes and pavement irregularities. You might turn a crack into a break with a bump but it was the many miles of riding before that did the damage.

Lighter spokes stretch more at a given tension and will tolerate more rim deflection before they go slack. Using them on the non-drive side of a rear wheel (regardless of what you do on the drive side) will let you get away with less tension before you have problems, but you're better off building the wheel right with sufficient high tension (the last rear Open Pro I built ended up at 110kgf with a tire on backed off half a turn from where stress relieving exceeded the rim's elastic limit. Deeper profiles tolerate more). If you do that even straight 14 gauge spokes will be fine.

In a lower spoke count wheel for heavier riders who might notice stiffness issues you can get away with lighter spokes on the non-drive side because the shallower bracing angle means the non-drive side spokes stretch more than the drive side spokes for a given rim deflection so you can use a more elastic spoke on that side for a given allowable lateral stiffness.

That said, 2.0/1.8 spokes are affordable (DTs can be had for under $.70 each), stocked nearly everywhere, and easy to build with.

2.0/1.7/1.8 are lighter, compatible with modern hubs, and shouldn't be much harder to deal with but are more expensive.

2.0/1.5 spokes are lighter still, cost about the same as 2.0/1.8, can be bought a lot of places, and are harder to deal with.

2.0/1.5 spokes which have been flattened weigh the same as their round ancestors, have a price tag 3-4X as high, net a few Watts at high speeds, and are cool.

Pick your poison. You won't notice the weight difference but can feel happy about having built a wheelset xx grams lighter than it could have been and looks cooler (if you use something really neat like aerospokes or rainbow anodized titanium spokes). I'll use DT Aerolites on my next set for that reason and because I've never built a wheelset with bladed spokes (32 hole Powertap 2.4+ with a brand new hub shell, 15mm axle, and once-again working electronics; 28 hole Powertap front; traditional silver rims and spokes; Kinlin XR-300 because everyone was out of silver 32/28 hole XR-270s when my Powertap broke and I was forced to get around to removing the bent rim needing replacement to save on shipping before the next batch arrives; cross-3 rear because it works, cross-2 front, conveniently produces the same spoke length for front and rear drive side so I can use 3 boxes of spokes for $50 each and 4 loose spokes at $3.50 each)