Dear Sir,

Please tell me about the electrical designing constraints / inputs. What are the basis of electrical designing

Please restate your question with more specific concepts of exactly what you are seeking. Your question is too broad and vague. We do not have time nor space to write the volumes of detail necessary in an attempt to touch upon the particular subject that may be sought.

Briefly:
Constraints in order of priority
Money
Time
Space
Input in no particular order of priority
OwnerOccupant
Engineer
Designers
Contractor
Subcontractors
Applicable codes
Municipalities
Manufacturers of products
Basis
Safety
Purpose
Needs

Why do you ask? Did you miss the first class of EE?