Estimating Full Rehab without seeing property

[Bert Cohen]

Newbie here. Would appreciate some guidance. We are looking at an off market property in an up and coming neighborhood in Philadelphia. It is a full rehab. Everything needs to be replaced. We are looking to make a substantial profit. Realtor wants highest and best tomorrow. Multiple offers. What tools/ methods do you use to calculate range of rehab cost?   This will be higher end rehab. Home 2,000 square feet. Will need additional bathroom added. Thank you for any advice you can give.