Question

If this creature was 50ft long, height 20ft tall, so the weight could be 10-12tons possibility or less? Though wingspan I have feeling 100-200ft from the height and length

Answer 1

It depends on what "50ft long, height 20ft tall" means. Is it an assumption that the creature can be represented by a parallelepiped of such dimensions (fig.1)? Or is it just a "box" where the creature can fit (fig.2)?

In the first case, the weight will be around 2000 tons. In the second case, of course, most of the space inside the box will be air, so, the weight will be around 10-12 tons. Most aircrafts capable of carrying up to 15 tons of payload have a wingspan of around 100 ft.