Page 20 of Booklet 3: Underworld and Wilderness Adventures begins the section on Construction of Castles and Strongholds and goes on to give prices and measurements to various parts of your stronghold most characters could begin building at 9th level.
This was an important part of OD&D not as emphasized in later editions.
I always felt this would have been done better as basic plans: buy a Tower, Stronghold, Mott & Bailey, Keep, Castle, Fortress, or Palace, etc. Then construct additional parts with the characters wealth later on.
In the illustrations in the booklet showing what your character could have constructed an essential part of all castles is missing: the 'privy chamber', or just 'privy' or 'garderobe'. Other names included the ‘draught’, ‘gong’, ‘siege-house’, ‘neccessarium’, and even ‘Golden Tower’. This was not only a necessary feature, but was also used in deterrence against sieges as they either emptied out into a moat, or directly onto potential attackers.
This also necessitated the services of a person to clean out the privy when it got too full or too foul to bear. This trade was called a Gong Farmer. After the term for "going" (potty).
Hit Die: d6
Prime Requisite: Constitution
Social Status: -2
Gong farmers specialize in waste management. They work primarily at night where they come to a house, dig out all the feces under a privy, and carry it to a dump where it can be recycled as fertilizer and building materials. These men are in high demand. They are only allowed to work at night, build up resistances to diseases, and are required to live far, far away from other people. But they are paid quite well (up to six gold pieces a day), making it worth working chest deep in unspeakable horror.
They Save and Attack as a 1st level Fighting Man.
The Gong Farmer could be used as a pre-adventure career for a character.
More details here: www.ancient.eu/article/1239/toilets-in-a-medieval-castle/