I am trying to learn how to program Computercraft Mining Turtles and I want to write a program that prompts the user for the side length dimensions for a cube which is then built. I use io.read() to get the user to input the side lengths and if he wants the cube to be solid or hollow via Y/N inputs. However when I check the answer to that last question I get a error that I have a table and need a string. 
Error code: Cube:17: bad argument: string expected, got table

Here's my code

```
--"Cube constructor"
--"Powered by UglySoft"

function get_dimensions()
  --"prompts for cube dimensions and Solid"

  print("Please enter the Cube dimensions.\n")

  io.write("Cube side length ")
  side_length = tonumber(io.read())

  io.write("Solid Cube? (Y/N) ")
  solid = io.read()

  solid = string:lower()

  return side_length, solid
end

function build_solid(side_length)
    print("Building solid Cube with side length ", side_length)
end

function build_hollow(side_length)
    print("Building hollow Cube with side length ", side_length)
end

function main()
    --"main part of the program"
    term.clear()
    print("Welcome to Cube Builder")
    print("powered by UglySoft \n")

    get_dimensions()

    if solid == "y" then
        build_solid()
    else
        build_hollow()
    end

end

main()

```

I am very new to lua and I am not even sure if I should use io.read() in this situation. Any help is greatly appreciated and feel free to ask questions.