Most real estate wrongs can be mended over time so the risk profile is less than you'd normally think as long as you are doing your homework and making sure you are properly screening for tenants. 10 years from now with rent hikes and other market factors, if you bought it wrong today but were just breaking even you will have built up equity and eventually cash flow because the asset and rent prices will have appreciated with a certain degree of confidence. 

My best advice would be to network with investors and find a reasonably priced roofer.

Quick opinion between two roofers.

The only issue I see with it is the inability to create expense categories such as "roofing' and label all payments made to the roofer tallied up yet separate to show the date and receipt for the individual payments.

I have both a trusted roofer and AC man ready to install.

While I don't normally like buying roofing materials myself, my roofer is happy to give me the list of stuff we need, and I can just fax it to Menards, they'll pull it and have it delivered, and then I receive a rebate check in the mail a couple weeks later.

.#3 Contact Local Contractors for Labor Pricing / Hire a GC to ConsultCall local Subcontractors and get budget pricing for common repairs on your typical rehab project.For example, call a roofer and ask what their average cost per Square of Architectural Asphalt Shingle Roofing would be on a 1,500 sf house, with a 6/12 pitch.Note: Some contractors will be reluctant to share pricing without seeing the property, but tell them you are just looking for a rough budget number you can use on future projects.You can also pay a General Contractor a consulting fee of a couple of hundred dollars (per house) to walkthrough a few properties with you and provide a detailed estimate of prices that you can use as your 'menu for future projects.#4 Compile Your Prices into a Spreadsheet or Estimating SoftwareOnce you start to get a better understanding of Labor and Material costs you will want to store this data into a spreadsheet or software that you can use to help you streamline the estimating process.The Book on Estimating Rehab Costs comes with a spreadsheet that you can use to help you populate your own database of labor pricing and material pricing.

Typically they will recommend that you contact a professional XXXXX (electrician, plumber, roofer, electrician, etc.) to get an assessment and estimate. 

If it is just the flashing, can you hire a handyman/woman instead of a roofer?

Call a roofer and get an estimate.