### Step-by-Step Guide

1. **Create a Directory for Your Docker Setup**

   Create a new directory on your local machine to store the Dockerfile and build script.

   ```bash
   mkdir custom-n8n
   cd custom-n8n
   ```

2. **Create the Dockerfile**

   Inside the `custom-n8n` directory, create a file named `Dockerfile`:

   ```bash
   touch Dockerfile
   ```

   Then, open it in a text editor (e.g., `nano`, `vim`, or any code editor) and paste the contents of the Dockerfile provided earlier:

   **Dockerfile**:
   ```Dockerfile
   # Start from the latest n8n image
   FROM n8nio/n8n:latest

   # Install dependencies required for Pyenv and Python builds
   USER root
   RUN apk add --no-cache bash curl git make gcc g++ zlib-dev bzip2-dev readline-dev sqlite-dev openssl-dev tk-dev libffi-dev linux-headers xz-dev

   # Set environment variables for Pyenv
   ENV PYENV_ROOT="/root/.pyenv"
   ENV PATH="$PYENV_ROOT/bin:$PATH"

   # Install Pyenv
   RUN curl https://pyenv.run | bash

   # Set up Pyenv in the shell environment
   RUN echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> /root/.bashrc && \
       echo 'eval "$(pyenv init --path)"' >> /root/.bashrc && \
       echo 'eval "$(pyenv init -)"' >> /root/.bashrc && \
       echo 'eval "$(pyenv virtualenv-init -)"' >> /root/.bashrc

   # Install multiple Python versions
   RUN bash -c "source /root/.bashrc && \
       pyenv install 3.9.19 && \
       pyenv install 3.10.14 && \
       pyenv install 3.11.9 && \
       pyenv install 3.12.6 && \
       pyenv global 3.12.6"

   # Set the user back to 'node' (default user for n8n)
   USER node
   ```

3. **Create the Build Script**

   Still in the `custom-n8n` directory, create a file named `build_n8n_custom.sh`:

   ```bash
   touch build_n8n_custom.sh
   ```

   Open it in a text editor and paste the following script:

   **build_n8n_custom.sh**:
   ```bash
   #!/bin/bash

   # Define the image name and tag
   IMAGE_NAME="custom-n8n"
   IMAGE_TAG="latest"

   # Build the custom Docker image
   echo "Building the custom n8n image..."
   docker build -t $IMAGE_NAME:$IMAGE_TAG .

   # Display success message
   if [ $? -eq 0 ]; then
       echo "Custom n8n image built successfully: $IMAGE_NAME:$IMAGE_TAG"
   else
       echo "Failed to build the custom n8n image."
       exit 1
   fi
   ```

   Make the script executable by running:

   ```bash
   chmod +x build_n8n_custom.sh
   ```

4. **Build the Custom Docker Image**

   Run the `build_n8n_custom.sh` script to build your custom n8n image with the desired Python versions:

   ```bash
   ./build_n8n_custom.sh
   ```

   This will create a Docker image named `custom-n8n:latest` based on the `Dockerfile` you created.

5. **Run Your Custom n8n Image**

   After building the image, you can start your custom n8n instance using the following command:

   ```bash
   docker run -d --rm \
       --name n8n \
       -p 5678:5678 \
       -e GENERIC_TIMEZONE="Europe/London" \
       -e TZ="Europe/London" \
       -v n8n_data:/home/node/.n8n \
       -v /home/J2897/Projects:/home/node/Projects \
       custom-n8n:latest
   ```

Now, you have a Docker image with n8n and multiple Python versions set up via Pyenv. When a new n8n version is released, simply update the `FROM n8nio/n8n:latest` line in the Dockerfile, re-run the build script, and your custom environment will be ready with the latest version.