Q.building container planter
Am building a container veggie garden (on legs, waist high) out of logs and wonder should it be lined with plastic liner with drainage holes cut to keep it from drying out quickly and help with cold or would there be a concern about toxic substances leaching from it? Also, will a ‘lasagna’ technique work in this?
You don't need the plastic to keep it from drying out. In raised beds like that, most people use it to help prevent damage to the wood of the planter from the wet soil. I personally do not have any concerns about there being toxic chemicals from the plastic, but I do know people who have concerns about using less than food grade plastic for food growing projects. For this, it is a personal choice.
A lasagna technique works well in these kinds of raised beds.