Tree with small roots?

Hi,
Can any one help me with a small problem. We need to plant a tree that will grow to cover a recent roof conversion that has a window directly over looking our entire garden. It needs to have a small root as we have a raised garden and a retaining wall. The tree will be planted near that wall.

If anyone has any ideas on what tree to plant i would be really grateful.
Charlotte

 

Buddlejia springs to mind, as it is extremely fast growing, low maintenance and will do ok in a large container.

How tall does it need to be?

EDIT: Just noticed you've just joined. Hi and welcome to GC.

 

Elders grow very tall and very bushy. Cut back quite hard in the spring. They also grow very quickly. There is a lovely light green feathery one Sambucus racemosa 'Sutherland Gold' and a dark leaved variety with pink flowers Sambucus nigra 'Gerda' or Sambucus nigra 'black lace' They are gorgeous planted together. The contrast in colours is lovely. The root system would not be so huge as to damage a wall. I have mine in a raised bed and have never seen the roots. they are very hardy large shrubs

 

Excellent suggestion. They are, in my opinion, far prettier than buddlejia too, and grow at quite a rate.