"a considerably big" is not grammatically correct.
However, you could say "considerably big" or "a considerable size." For example, "The elephant was considerably big" or "The building was of considerable size."
Despite such large-scale live appearances, Strictly Come Dancing will bring a considerably bigger audience.
So unless we can somehow extricate ourselves from Iraq quickly, or persuade other countries to bear a lot more of the burden, we need a considerably bigger military.
The World Cup final at Twickenham later this year will be a considerably bigger event than the Champions Cup final staged there last weekend.
There were no accidents on the carousel and no problems with electric doors this time as a considerably bigger crowd greeted him.
Agents and distributors come calling, helping to propel the director into a lucrative Hollywood career and a considerably bigger budget for a second feature film.
Khan has no world title but a considerably bigger US profile having fought there eight times over five years, and he clings to hopes of challenging either Floyd Mayweather or Manny Pacquiao.
Despite unctuous protests about good taste, there is an audience for this fight, a considerably bigger one than there had been before they came to blows in front of the cameras and some distance from a referee.
East Coast is a considerably bigger firm and Grand Central was not able compete on the number of services offered, although it has already announced plans to add more in the near future.
For the second Test there is little doubt that Moeen Ali, a considerably bigger spinner of the ball, will resume his all-round duties, Anderson's triumph has involved a long, arduous journey for him over almost a dozen years since he opened his account at Lord's in his first new-ball spell for England by rearranging the stumps of the Zimbabwean opener Mark Vermeulen.
