Can I still claim expenses for a major renovation as a self employed person with a home office if it puts me in the red?

Thank you for your question.

Yes you can claim renovation expenses on your t2125.

Please read this link to know which expenses you can claim, and where you will need to  put them on your T2125 form.

Be sure to be eligible to this deduction first:

http://www.cra-arc.gc.ca/tx/bsnss/tpcs/slprtnr/rprtng/t2125/menu-eng.html

Have a good day.

Where exactly do I enter the expenses.

Assuming you have clicked on self-employment, and have accessed the T2125, you can put office renovations under office expense, or other expenses.