import os
from typing import List

def create_project_structure(base_path: str, folders: List[str]) -> None:
    """
    Creates a folder structure within the specified base path if it doesn't already exist.

    This function iterates over a list of folder paths and creates the corresponding directories 
    within the specified base path. If a folder already exists, it skips creation without errors.

    Args:
        base_path (str): The base directory where the folders will be created.
        folders (List[str]): A list of folder paths (relative to `base_path`) to be created.

    Returns:
        None: This function does not return a value.

    Raises:
        OSError: If there is an issue creating any of the directories, an error message is printed.

    Example:
        create_project_structure("/home/user/project", ["data", "logs", "output"])
        This will create the following structure if it doesn't already exist:
            /home/user/project/data
            /home/user/project/logs
            /home/user/project/output
    """
    for folder in folders:
        folder_path = os.path.join(base_path, folder)
        try:
            os.makedirs(folder_path, exist_ok=True)
            print(f"Folder '{folder_path}' created successfully.")
        except Exception as e:
            print(f"An error occurred while creating the folder '{folder_path}': {e}")

# Example usage
base_path = "."
folders = [
    "data/",
    "data/eurostat/",
    "data/istat/",
    "llms",
    "modules/",
    "schemas/",
    "test"
]

create_project_structure(base_path, folders)