is it possible to build a Cessna 152/172 from spare donor parts etc?
Yes
In terms of getting a C of A and all the correct certifications would this be possible ?
Depending upon the nation, it would vary from hard "no", to "very, very difficult". "Easy" or "economical" are out of the question.
The absolute only reason to build your own plane, would be if you really enjoy building planes as a pastime, and are very knowledgeable about doing it. Otherwise, if simply flying the plane is your objective, buy or rent one in flying condition. Building a plane is an excellent way to become really conversant with building and maintenance, but if you value your time at all, no way to save money to fly one. It is certain, that you can buy a flying certified Cessna, for less than the cost of buying one airplane's worth of airworthy parts, let alone the effort required to assemble it, and letting alone the complexities of having it inspected and approved. Any used part for a certified requires authoritative "previous certification", without which, the part is virtually useless. And with it, the part can still be useless, depending upon its condition, and AD/SB compliance.