Building up second hand frames to resell I have built up a bike for myself recently and really enjoyed the process. Now my built is finished, I wish to work/build more bikes. I do not wish to do this full time or as my job, I would just like to work and tinker on bikes in my free time.
Would I be able to make ( small ) profits or even break-even when buying lose parts ( frame, wheels, groupsets, ... ) and building them up myself to sell?
I only wish to work on/build bikes as a hobby, but can't afford to buy and own multiple bikes. Is it possible I can turn break-even or make very small profits ( even $50 or $100 ) after selling complete bikes? I am not doing this to make money, I just can't afford to lose any on it.
! Not taking into account the tool I buy, since I will be able to re-use them on my own bike or bikes from friends. Not taking into account the hours spent, researching and looking for parts or even building the bike up.
There could be some sticky points with what you propose in that even though you won't see what you're doing as a business, your customers probably will. You'll be accountable to doing right by them and there will be times when that will feel like work, be work, and cost you money or time like work.
The answer to your question also depends entirely on what you're paying, if anything, for the bikes and parts you're working with. In some times and places, old bikes in need of work that's hard to time-justify outside of being a labor of love are abundant. But if there's a strong used market, maybe not such much.
A very good avenue for the passion you're talking about is getting involved with community or nonprofit bike shops as a volunteer. Most cities have organizations or businesses in this vein, and most of them welcome volunteer labor to make sellable bikes out of their old parts. And, they typically have proper insurance and other trappings of actual businesses in place, which are all other ways the outside world could expect you to be a business even if you don't consider yourself one if you're just doing it on your own.
Some of these community initiatives keep a very low profile, often without any web presence, and might be tricky to find. They are sometimes side projects at various charities (focused on homelessness, substance abuse or prisoner resettlement), schools, churches or even squats. It's definitely worth asking around in local bike shops or clubs.
If you don't have a community bike shop or project nearby, consider starting one. But the time you've done all that asking around you will likely have some contacts etc.