Here's an outdoor coffee table project from a fellow hometalker. You could simply modify the dimensions to make it suit your needs. Good luck! https://www.hometalk.com/31634800/diy-outdoor-coffee-table
What materials do you want? There’s many things you can re-work and re-purpose.
How much exposure will it get to rain & sun, year round?
Do you expect to put potted plants on it and water the plants on the table?
Here’s some materials considerations:
Wood? It should be pressure treated, unless your porch is very sheltered & you paint or spar varnish it.
If you don’t mind if it doesn’t last for 10 years, then re-purpose a piece of furniture.
Metal? Once again, finishes like galvanized or primed & painted.
Galvanized plumbing pipe & fittings are creative, cheap, strong and long lasting. I suggest lightly greasing the joints before assembly.
Plastic? A lot of plastics break down in the UV and I’d consider how long I expect it to last. For example, Assembled PVC plumbing pipe must be painted and zip-tying plastic crates together has a finite life.
Like the galv pipe, PVC pipe is a very creative media, although, not as strong for the spans - but can be drilled for small additional options. Requires proper primer & glue.
If using any of the pipe-options, sketch out the connections & the span lengths and do a count before going to the big box DIY store, where there’s often no help available.
Here is another Hometalk idea! If you wanted this as an exterior table you could stain it and add 2 coats of marine spar varnish over it for exterior use. https://www.hometalk.com/36375287/farmhouse-entry-table?expand_all_questions=1
If you want to use wood, marine plywood and other wood you would need is the way to go. It is made to be in the weather for any climate. Finish it off with marine poly in many coats and it will last for years. My hubby made me castor platforms for my large planters, as many come into the house for the winter or need to be moved around, out of scrap marine plywood. We never did anything to them but put the pots on them and I have been using them for two years. They are getting some staining from water running over them, but they are as sturdy as ever and should last for years.
Sandy...I have seen many made with pallets!