have been thinking about almost completely covering this side of the pergola and leaving the ends and pond side open and maybe getting some clear plastic covering for the top, or adding a peaked roof with tin roof, the wavy kind. not sure how to cover that side that faces the road, horizontal posts? vertical panels? metal rails? not a fan of cheap looking attic but need some way to enclose this somewhat. have considered enclosing 3 sides. just not sure what to do to make this look good and a place to hang out next to the pond. we are in west Texas so summers are pretty hot. this is north of the house next to a Grove of mesquite trees

Currently the pergola seems disproportionately tall and narrow. I wouldn’t add any additional height. How are winds in your area? If you add a roof covering, it will need modifying to give the roof some pitch, perhaps by slightly lowering one side. It may need some additional bracing if either a roof or sides are added in order to be structurally sound in windy or stormy conditions since it wasn’t built with a solid roof or any walls. So I think modifying the structure in these ways may not be what you want to do since there is a fair amount of potential expense.

I would start by considering tall plantings in beds along the sides to help ground it and to provide screening from the road. In the near term, outdoor curtains that can be drawn when you want screening may help while the plants grow.

"... have been thinking about ... [you go on to list many possible alterations.]

Are these alterations simply to solve the title issue ... appearance? If they are, I would not do any of them. You also do not say why you need to "enclose [it] somewhat." If you just turn it into a functioning arbor/pergola by growing a vine on it, you'll get shelter from the sun and a few minutes of protection from rain. If you need functionally more than that, then say what it is you're trying to achieve.

Insofar as appearance is concerned, the arbor is under-built, as the beams are sagging. I'd add a center post at each long side to take care of that. Additionally, standard traditional arbor details such as brackets at each post would add interest to the appearance and a lot of strength to the overall structure. (If it were me, I'd add beams and brackets at each end of the arbor, too (which would take too long for me to include in the drawing... as well as would probably muck it up.)

Last but not least, the arbor currently has the texture and color of a scab healing over. It would look immensely better if painted (with gloss acrylic.) White is a standard color, but it can be something else if that works for your surroundings.