I think that if you have never built one, you should google 'Porch swing', or 'garden swing', to see if you can find some free plans. If people are going to use it, the support needs to be substantial. Here's a picture of my swing. There are no plans for the support structure, but I have built several over the years.

You might also google 'Free Plans'.

Hope this helps.
Jim

{{gwi:683}}

My father made me one last year.

Here is a link that might be useful: