Create a subsection of Castles called Land.
Create a subrule of land wich reads:

Each Vassal has publicly-tracked number called land area.(hereafter also refered as land)
The starting value of land is 100. Land is expressed in hectare and follows the metric system. Land is spendible and can’t be less then zero. An action is legal if a player must pay amount off land but is its value is bigger than the current amount of land that Vassal has.

Create a subsection of structures called special buildings.
Create a subrule of structures wich reads:

Special buildings are structures that are not part of the castle nor have a defensive stat or theatre.

In the table materials add the following :Food
Add a rule to stockpile wich reads:

If a vassal must remove a food but the number is zero he is unable.

Create a rule of special buildings wich reads:

{| class=“wikitable”
|-
! Name !! Cost !! resource

|farm|| wood, 10 hectare|| A farm produces 2 food plus 2 food per extra size above the first.

Create a bullet point in the Fortnight subsection as 3th wich reads:

For each serf a vassal has above 5 he must remove 1 food. For each food unable to remove he losses 1 serf.