I’m considering the “Build Me Up” plan. I’m also thinking about incorporating some running and outdoor cycling into my routine. Would this be alright in terms of avoiding overtraining?
How many days of intensity do you do on the bike already?
Personally I found Build Me Up to have too many days of intensity for myself even without doing any other days of intensity outside of Zwift, but I think for me the sweet spot for intensity is 3 days per week or fewer.
Thanks for sharing your experience! Currently, I’m doing the “Build Me Up” plan, which consists of 4-5 workouts lasting 1-1.5 hours per week, with 3 workouts on rest weeks. I’ve occasionally added treadmill runs and outdoor rides when time allows, but so far, I haven’t encountered any issues. However, I’m definitely mindful of overtraining and want to take precautions to avoid it. Your input about keeping intensity to 3 days per week or fewer is helpful. I’ll keep that in mind as I continue to fine-tune my routine.
Where Build Me Up became an issue for me was about week 7 into the plan. That’s where I started dreading getting on the bike daily, and started questioning my life choices 
Edit: But some folks are fine with it, some folks can just smash it every day, I’m not one of them.
I’m glancing at the plan. Typically, I think a lot of people would schedule 2 harder structured sessions and at least 1 longer endurance ride. The balance can be recovery or more endurance.
I think the 12-week FTP builder adheres to that format.
It does not look like Build Me Up adheres to that format, so I see what you mean.
For the OP, I think I would substitute some of the workouts for runs. I’m not sure what intensity you plan on running. I would probably choose two workouts that were hard but not challenging, and then some manageable mix of runs and outdoor rides. If you planned on running intervals, then maybe only choose 1 of the BMU workouts.