Hello. i am a solicitor with 20 years experience. I will try to help you with this.
Did you view the property before you signed the agreement? Are there any specific clauses dealing with maintennance and disrepair problems like this. I doubt whether either of these problems would enable you to cancel the agreement. The pi tin the garage would usualyy be covered by caveat emptor. The windows in poor repair may well be a breach of the repairing obligations of the landlord but are viewed by the law as quite minor Did you notice them before hand and require them to be fixed before moving in or make security a particularly important factor in taking the tenancy? If so things might be a bit different.
Ok did he agree to make it secure? Even if he did then this is unlikely to be such a serious breach that you can abandon the contract. Your better bet is to try and gt the repairs carried out.
I am busy with my children on and off this morning but will get back to this site later today.
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