Try looking at some pictures on gardenstructure.com. The most common and economical choice will probably be wood which could be painted a funky colour, or Lutyens built them from tiles in a tall pile with wooden 'rafters' on top. Or Agriframes sell metal structures that can be fitted together in any length that you would like. Consider also, what, if any, type of plants you would like to grow up it as this can affect your choice, otherwise you have to attach wires/netting etc.

Hi Vally lots to choose from flat or arch topped wood or metal, quality, durability and maintainance depends on how much you spend? - google them for lots of pics and ideas. I am asuming you want to grow against it? lots of plants suitable but you need to think about how you want the pergola you select, to look when its empty or covered such as bare in winter or evergreen? See through or dence shade? Spring flowering or all summer? Winter leaf colour? Also consider will the path be slippery if shaded and damp?
Perennial Sweet Pea (Lathyrus latifolius) saw this in the summer worth considering? Good luck