Question
How many tree are cut down to build houses every year?
And

How many trees would be left by year 3oo4?

Answer
I think you have been mislead in to beleiving that there is a shortage of trees. Not knowing where you are or your back ground, I am going to use data from the US in the Alabama. The first fact to remember is that trees are a renewable resource and when one is cut others are planted or seeded in naturally. So whatever nunber of "trees are cut to build houses" there are other trees planted to  take their place. The fact is there are more trees and acres of forests now than in the early 1900's. In Alabama the following is true:

 71% of Alabama is covered with forests.
Alabama has the second largest commercial forest in the nation.
There are nearly 23 million acres of forest growing over 16 billion trees

  
 -How Many Acres is 23-Million?
    Alabama's Forest is approximately the size of the state of Indiana!
 -How Many Trees is 15 Billion?
     Alabama's Forest grows 4,000 trees for every man, woman, and child in the state.
 -How Much Wood is in Alabama's Forest?
    Currently, enough lumber exists in Alabama forest to build and furnish nearly 4 million homes.

Other data about the amount of forest and the fact that we have more now than in the early 1900's can be found at:
http://abcnews.go.com/sections/2020/US/myths_040322-7.html
This a piece that was on ABC's 20/20 concerning the myth "Are we distroying our forests?"