Describe the stay before the building
Start with how many people will stay, which seasons you want to use the place, and what you will do there. A reading retreat and a remote working base need different plans. Note which comforts matter most and which you are happy to simplify. This is your brief for the project, not a shopping list.
Make a site questions list
Record access, the condition of any existing shelter, exposure to weather, available services and who can answer local questions. Before committing to land, building work or a wastewater arrangement, establish which local permissions and professional assessments apply. Keep an unanswered requirement visibly open in the plan.
Connect the everyday essentials
Sketch a normal day: arriving, making food, washing, using the toilet, sleeping and leaving. For each activity, write what the place already provides. Add the missing arrangements to the relevant part of your project. Think about wet clothes, muddy footwear, storing food and getting supplies to the site as well as the larger equipment.
Plan the empty days too
Decide what will be switched off, what must stay working, and who will notice a problem between visits. Give every proposed system an arrival check and a leaving step. A modest setup with understandable routines is a useful starting point; add complexity when it solves a specific difficulty.