First --- I will clarify mysefl not from your state , So I have lot limitation , Still most law of all state are similar I will try this query
Second --- Regarding technical aspect. Local govt. sanction plan . It is accompanied by Commencement certificate and Building /house approved plan. Any thing which is not according to Plan is illegal. May be under circumstance ground floor can be illegal but first floor lega. because ground floor there can be parking space in Sanctioned plan
Third---- Whatever your purchase should be proper in Sanction pland as well if completion of structure is over then Completion certificate and Occupying certificate has also attached plan , that have to be checked and verified whether it is legal or illegal , Portion of house or building whether you take is legal or illegal
Fourth --- Risk of taking illegal. General case people feel nothing can happen to them , People also say instead of demolishing they are charged more property tax (Municipal Tax) and thus they are legal. It is all wrong , Tomorrow situation comes that land is required for road widening purpose or for some high way that time illegal people or structure don't get anything or rather neglible. Even if there is legal dispute people go and complaint to local govt. and try to get structure demolished instead of court procedure.
Fifth --- All people who are residing in illegal structure many times become victim of politician Hafta vasuli. May be they will ask this way or that way but many times it is observed people have to pay and please local politican so their strucutre is safe from authorities who have powers under various laws to demolish illegal structure.
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Some time I feel person should not invest in illegal things for residence , because in your absence your spouse , children are at high risk. Commercial may be wrong , but their people thing economially and use for giving hafta to govt. officers .
This is all what i can state about illegal structure and things going on every where
