To ask how you would improve this roof terrace?!

[TheFUNword]

Please :)

Pinterest will give you lots of ideas, or easy stuff like:
Paint wall white, to make space look bigger.
Lots of lavender, pink & yellow roses/geraniums in terracotta pots for contrast.

Jasmine, camelia, wisteria climbing up trellis on wall at either end or all along depending on taste.
Depending on budget/taste/ views, glass or wrought iron railings at front
Pretty Iron patio set in dark green, or blue or white.
If possible I'd remove 1970's flagstones, replace with small oblong reddish bricks & gravel edging.
Mini 'aged/distressed' stone water fountain on wall is nice, but no idea re cost, how much hassle to fit tho.

Paint the wall white

Repaint the fence white

Jetwash the patio slabs, they look a bit manky

Lots of greenery in pots dotted around

A nice colourful metal patio set or a rattan one if you prefer (just not plastic!)

If the terrace can take the weight then planters alone the wall,big one with liners they will he easier to manage watering than just pots.Rather than paint the wall use it to grow plants up ., roses, honeysuckle,jasmine,French or runner beans whatever you want.More planters along the lower fence with herbs,veg.You can make it as low/high maintenance as you want.
A decent table and chairs with a parasol or awning for shade.
I would also sort a washing line or rotary drier fix.And if you have room against the other walks a storage bench to keep hose,pots,watering can and furniture covers in.

Try not to paint the wall white because white looks dirty really easily. I'd be looking at painting the wall a bright colour like orange, red or turquoise. For the fence, id paint it black and check if it's high enough. To be kid safe I'd look at making the slats closer and adding a third one to the top. Depending on how windy it gets I would look to add a trellis as a wind breaker. If you paint it dark green it will blend in with the foliage of the trees.

Finally I'd get some good lighting up. Not fairy lights but the bigger outdoor lights which you can dim or brighten depending on your mood.

White wall. It does fade and we have to redo ours every couple of years so it depends on how much maintenance you want.

Lots of brightly coloured and scented plants in them. A good plant nursery can advise on which to buy so you have flowers at different times of the year, but you need to tell them how much sun the area gets.

You could put some trellis up with climbing plants such as sweet peas or clematis. Clematis will spread horizontally if you don't have much height to the wall.

Lavender is a good one for colour, smell and seems to do well in our garden where it's exposed to wind and sun.

For furniture, I'd go for metal that won't rust so you can leave it out if you don't have anywhere to store it.