Can we construct a binary tree with width and height Θ(n)? we know this definition:

Given a binary tree, Width of a tree is maximum of widths of all levels.

Let us consider the below example tree.

     1
    /  \
   2    3
 /  \     \
4    5     8 
          /  \
         6    7


For the above tree,
width of level 1 is 1,
width of level 2 is 2,
width of level 3 is 3
width of level 4 is 2.

So the maximum width of the tree is 3.

can we have a binary tree with Height $\Theta(n)$  and Width  $\Theta(n)$

My solution:
is YES. for example a binary tree with one-node: 

     1


am i right?
Statements about $\Theta$-classes are statements about the behaviour of an algorithm/data structure, as (in this case) $n$ gets large. Thus, a single example can never prove such a statement. You'd have to provide a set that contains examples that become arbitrarily large and behave as desired. (The set, however, doesn't have to contain an example for every value of $n$.)

So you should try to construct such a set of examples. (And if you fail constantly, try to find out why. This might lead to a proof that no such set exists, i.e. the claim is false.)