I agree with Bazyle and Phil.
The tar paper is not a true DPM but if any water gets in through the FE boarding the paper will stop the water reaching the structural frame.
You can use fibreglass or rockwool between the timbers and line internally with foil backed plaster board or a decent vapour barrier overlaid by a lining of your choice. The foil helps reduce heat loss through radiant heat too.
What tends to get overlooked by Building Regulations (and the BREAMM energy performance model) is that buildings do not often sit in a steady state – they get wet on the outside, get exposed to dry winds which cause wet surfaces to evaporate water quickly (chilling them), and get erratically heated and steamed up internally.
It has been shown that thermal mass is also important in control of moisture. A 'breathable' masonry inner surface and unsealed concrete floor will take up moisture in the short term and gradually release it when internal air is dry.
This effect can be useful as our machines have very high thermal mass and will suffer from condensation when their temperature remains below that of the dew point at that time.
Keeping the workshop reasonably heated will overcome this by keeping the temperature above dew point, but having the fabric able to absorb moisture will help keep dew point at a low temperature (by helping keep the air dry)
It is a complex subject but if going the low thermal mass / low heat input route I would advise to ensure robust vapour barrier and well sealed doors and windows combined with a dehumidifier. Be careful with fumes in such a building!