You will either complete this goal in a village where Stonecutters can naturally generate, or crafted yourself. In order to memorise the Village houses so you can spot a Mason house in Bird's Eye View or from afar, you can visit this house guessing site by Sam.
Stonecutters are crafted with 3 stone (smelt cobblestone or silk touch pick) and 1 iron ingot. Note that the Bedrock recipe that allows you to use other stone variants is NOT in Draftout. While you must get 3 cobblestone to craft the Stonecutter, you needn't necessarily get a fourth to cut if you ran into Diorite/Granite/Andesite on your dig-down.
You can also hang onto bricks if you had e.g. Fill a Decorated Pot to craft bricks to cut. This only saves you a very short amount of overlap time with the smelting though, so it can be good practice to just mine 1 extra cobblestone.
One of the most straightforward methods. The house has bottom slabs for a roof with 4 cut sandstone sticking out in the corner, note the difference to the Library and Medium House. It has a long flat half-block window at the back, but despite these windows it's easiest to access the Stonecutter from the inside. The Stonecutter is against the right hand wall.
Punch 4 sand before getting to the house and craft them into 1 sandstone block, which you can cut in the Stonecutter.
The Mason house in plains villages is quite distinctive, being only 1 of 5 houses that use Terracotta, and easily differentiated from those. Again, the Stonecutter is against the right hand wall, and can be accessed through the front, side or back windows if needed.
If you have a close Mason villager, your best option is to punch 3 of the clay blocks in the house, trade for an emerald and then trade for bricks. You can craft these bricks into a brick block which you can cut with the Stonecutter.
You don't have to get the emerald this way, you can check chests on the way.
If you don't have a Mason, you will likely have to punch 3 logs, craft a Wooden Pickaxe and mine a cobblestone block. This can be one next to the Stonecutter in the floor. Note that you cannot cut Terracotta.
If you can see the Yellow Glazed Terracotta that's a glaring sign, but otherwise this is the only house with a sort of oval shaped roof like this: all the others are more square or rectangular. In contrast to the previous 2, the Stonecutter generates on the left hand side.
Your first move with this house should always be to check the chest, which you can access from inside, or through the back right or right side windows. You have a 70.82% chance for a Stone Brick/Stone/Smooth Stone block which you can cut.
As a backup, you can use any emerald/clay from the chest/clay from the 6 blocks in the house to trade for bricks, or in the absense of that, punch 3 wood and dig for any stone.
The only Village with 2 Masons. These are probably the least distinctive of all the Mason houses, but the overlapping roof/porch in Masons House 2 is quite recognisable. If you can get any emeralds, then trading with a Mason is viable, but forcing this is likely to be slower than crafting a pickaxe.
Masons House 1 has no stone blocks. It has a Stonecutter on the right hand side opposite the furnaces, accessible through the back window.
Masons House 2 has Diorite blocks that you can Cut. The Stonecutter is the left.
This House is a good one to remember, the roof forming a triangular tent shape. The Stonecutter is straight ahead on the inside and accessible through the back window, and there is cobblestone that you can mine to cut.