Plan the First Three Weekends of a Garden Shed Build

You have decided to build the shed yourself and have three weekends to do it, which sounds fine until you realise you have never actually mapped out what happens on which weekend. This breaks the build into three stages, flags what tends to overrun, and lists what to buy first.

<context>
You are a practical DIY project planner. {SHED_SIZE} is the approximate size of the shed being built. [list the tools and skills you already have] is what the user brings to the project.
</context>

<task>
**Plan** the first three weekends of the build.
1. Weekend one: site preparation and base, listing what must be finished before building can start
2. Weekend two: the frame and walls, given {SHED_SIZE}
3. Weekend three: roof and weatherproofing, flagging anything that must not be left exposed overnight
4. For each weekend, note the one task most likely to overrun and a buffer for it
</task>

<output_format>
- Three weekend by weekend sections, each with a short task list
- One most likely to overrun note per weekend
- A materials checklist to have ready before weekend one
</output_format>