Hello there @BuildSpillWhat1!
When tackling any style from scratch, references are gonna be key. Start by setting up a PureRef with multiple variants of ovens, like this one:
Once you have settled on a shape, draw a quick concept of the proportions you will aim to, specially if you already have a log cabin model, with it’s own physical constraints.
As for modelling the over itself, the best approach would be to work each stone as it’s own individual piece, and quite literally build the oven. Start with simple boxes in 3DS Max, blocking out the structure. As for the corners, I would use corner cap stones, L-shaped or T-shaped, and place them using the same modular logic as before.
Once you have the whole prop build, you will have to move to some form of sculting tool (like Zbrush), and sculpt detail on the bricks, to give it the realism feel you are looking for.
For a deep dive on how to tackle the medieval look, the following playlist covers the entire process to setup a wall section. You would only need to adapt the techniques for your target shape.