You can either use the SQL Server Management Object API (see task “creating, altering and removing databases“):
var srv = new Server();
var db = new Database(srv, "mydb");
db.Create();
Information on how to get started is here. During SQL server installation you need to install the client SDK, the SMO assemblies are in C:\Program Files\Microsoft SQL Server\100\SDK\Assemblies
Or if you don’t want the dependency on these assemblies, you can also simply run DDL statements using ADO.Net (e.g. see this question):
using (var connection = new SqlConnection(myConnectionString))
{
connection.Open();
var command = connection.CreateCommand();
command.CommandText = "CREATE DATABASE mydb";
command.ExecuteNonQuery();
}
Obviously you need a correct connection string: known sql server instance and a user with CREATE DATABASE permission.