Scratch built tunnel portals

Can anyone point me in the direction of scratch building tunnel portals besides the information station. I can’t bring myself to spend six bucks on information when there are model railroaders that have a wealth of knowledge and may be willing to share that information. Besides, my six bucks goes towards a new kit from a hobby shop. Please help! I am looking to build a simple in city portal.

I built a form using tin foil, popsicle sticks and a hot glue gun. Can’t really desribe it without pictures. It turn out OK.

Years ago, not on my present layout, I made a mold with modeling clay, shaped it till I got a portal I liked and poured plaster into it. Made a nice portal. By hand after that I carved in a date over the entrance like you see many times, scribed in some areas to look like stone foundation blocks . It actually looked very nice. If that is what you want try it, it’s easy. You can then stain it with what ever you like to use.