One issue is what the local authority will charge you for permitting and costs etc.

A quick $15k investment into a rehab house to turn $20k profit in 60 days, no permits.  

What are the laws on direct mail marketing in Sweeden, is that permitted?  

Sometimes it might take a few days more because of waiting for permit inspection, but that shouldn't be a problem.Honestly, I'm happy to find a property with a dead/damaged/missing furnace. 

Make sure the addition is permitted first.

My GC has stated that since he is the one pulling permits, i wont be allowed to do anything to the house since he is liable for anything that happens on-site. 

If time permits, consider visiting local investment clubs, you'll have an opportunity to meet other investors both new like yourself and seasoned.  

You may find some info by checking with the city's building planning department, ask them if any permits have been pulled on the property, otherwise trying to contact the last owner somehow might be another way.

SD is among the slowest I have dealt with when it came to permits.

They had a whole crew of code enforcement and permitting personnel visit the property (including the big code boss), and someone of them suggested that the frame was not salvageable.