then we are going to use exploratory testing technique.

then we go for adhoc testing

it is important to consider testability as a key (but 
usually nodocumented) requirement for any software 
development.

ya.I agree with Sumitha.if we dont have any proper 
documentation we can go with ad-hoc testing.

1.Better ways to analyze the application focus i.e. why the
application is being created in short "utility".
2.Past Experience will do the trick & we can apply ad hoc
measures to that functionality knowing pros & cons of the
implemented stuff if it is inline with the requirement to
fulfill the utility.
3.For such cases generally client always provided a referral
site saying " I want to get site designed like this."

or 

we need to follow Prototype model. 
1. Create the design template of application 
2. Demonstrate the template to client.
3. Refine the SRS.
This process will continue till final SRS is approved from
client