Database Level Lock

Hi,

How do I lock entire database? I want an exclusive lock on the db by
a user
who is the dbo of that database only (not sa
user).

The
scenario is we have a web application and each week we need to do data
uploads (with etl). During this upload, the users accessing the website
should not be able to read data. This is why I want database lock.

Now
the catch here is, the application access the data using user say abc.
Abc is dbo for that database and the etl is also done by abc login. So
will db locking help in this case as the website can also read the data
being a abc user?

Thanks,
Tanmaya