1)  if landlord neglects to carry out repairs tenant can issue 15 days notice to landlord and on his failure tenant can carry out the repairs and deduct the expenses from rent payable . the amount deducted should not exceed one fourth of rent payable .

2) you do not need landlord permission to carry out tenant able repairs

3)  Tenantable repairs as defined by section 342 of the MMCA, includes providing guniting to wall structures, plastering, painting, flooring, repairing of the bath, WC and wash places and replacing electrical fittings and several items

4) you cannot increase the height of structure 

First you can collect the evidence of all problems/issues you are facing and make complaint against landlord and developer against that construction which is made to next to your house or not to keep any debris and ask them to keep that area clean. Instead of keeping debris ask them to plant of flowers plants in the pots in that area.

Give the complaint in writing to BMC ward officer and do keep in cc to vice-commissioner, commissioner and corporators all four corporators of your wards.

Take the help of corporator who is working against landlord and Developer.

Regarding your rent is not accepted by Developer then kindly pay rent in the court.

You need to approach court for seeking directions for repair stating dilapidated condition of property 

The tenantable repairs can be carried out by yourself by issuing a notice to the landlord.

The repair charges can be deducted from the monthly rental amount every month to th4e extent of the permissible limit. 

If the landlord/developer stopped receiving the monthly rental amount, you may add that subject also in the legal notice and after that you can deposit the monthly rental amount with the rent control court regularly to avoid eviction for default in payment of monthly rental amount. 

Take legal proceedings against landlord to grant permission for flattening of roof 

You can go as per the Indian Easements Act, 1882  Section 8. Who may impose easements.

Try to repair its your rights to use the property. 

You need to approach civil court 

You can initiate legal steps for getting the property repaired/renovated.

You can issue a legal notice to the landlord/developer mentioning your concerns in this regard and demand letter of consent, if they do not respond or reject your demand/request, you can approach the authorities concerned requesting permission to proceed with the proposed activity.

If you do not get a proper response from the authorities also then you can approach court with a suit for mandatory injunction to permit you to carry out the repair work which is essential for inhabitation.

if the problem you have described in your query is a genuine claim which has caused nuisance to you such that because of the pest and water seepage and leakage your health is being affected and despite all that the corporation is insisting for noc of the owner to grant permission for making the changes as required by you to prevent the nuisance, then you will have to file a writ petition in the High Court seeking a direction to the BMC to dispense with the requirement of the noc letter from the owner

in that petition you will have to make the owner also a party respondent

before you file the petition you will have to make a written representation to the bmc about your plight with photographs attached to the letter

if within a reasonable time of receipt of your letter the bmc does not respond then you can approach the High Court by filing a writ petition