Aluminum dome roof

We are thinking to convert some of our external floating roof tank to Internal floating roof tank by aluminum dome roof. We already have some related documents. But we are not very much sure about the feasibility of the conversion. So I hope forum members will help us in this regard by providing some info like:
1. The approximate costing data
2. Disadvantages of such dome roof
3. Longevity of such roof.
4. Name of reliable company in this field
If anyone has related standard pls mention.
Thanks in advance.

first u reply why the crude tanks have external floating roof instead of internal floating roof mostly?

dear:
you can see our products maby can get some help.

[url]http://www.float-tek.com[/url]
[url]http://float-tek.com[/url]

Tks