I agree with the suggestion that John made about a local recycled materials store- Another good option, (and this might sound strange to those outside of urban areas- ha!) but most municipalities have a specific day-sometimes once a month, where individuals are allowed to throw out "bigger" things (things they might have to take to the dump for instance, like....gutters (that perhaps a more affluent person is changing due to...deciding to get all new siding in the color of periwinkle... who knows. another man's trash is definitely, (at least for me) my treasure. I have gotten some fabulous, good condition (minus some chippy paint) heavy and old single pane windows for free, pots, furniture (that might need a coat of paint- avoid mattresses or cushions (bedbugs!) and since people put these out on the corner during this day- they don't want them. Trust me, they are psyched to see you take them.......away. I have been doing this since I was in high school (always loved thrifting and garage sales) and I have never once had a person object to things they put out on "large garbage day"- Of course, if I walk by and see an item, and they are outside, It is the right thing to do to ask- but I have even been walking to the local pharmacy, seen something cool, I luck out, and the person is outside watering their lawn, tell hem I am a neighbor and could use their windows (for my cold frames!-or whatever) and I've even had nice folks let me set the items aside and go get my car. I am not sure if you live in an area where this is a possibility, but most smaller towns have at least one or two of these "bigger trash days" on their calendar.
I also in the past have gone to various thrift stores, or (even better) a recycled materials store, and not even that long ago, I desired some building materials for some projects around the house, my husband and I had just bought our first home, and I didn't want to spend any more money for awhile- So I went into the charity, and I asked if I could volunteer on busy days (trust me they always need help) and if I could in exchange for a day of volunteering- obtain a few thrift items. I guess that isn't necessarily "volunteering"- but the manager of this store looked like I had offered him the golden ticket. I did it a couple times, and I was able to put aside a very nice 1940s armoire that I wanted, and after 3 days, I was able to get it- This might not work if you have another job, but It felt good to help an organization doing good things, and since many folks don't want to work on the weekends, (or they are constantly understaffed with employees that they can't pay hardly at all) I was able to be useful and help sell items- and get that piece of furniture I wanted. Everyone was happy. Just an idea. You never know.
Recently, still on this, "try to make improvements for no cost, or hardly any cost" tip I am on with my house, I was cruising my local cragslist in the "materials" section. I had never really checked it out, and, of course, there are some folks who are selling their unused home renovation materials, and trying to get what they paid at Lowe's for them, (or make a profit which is kind of bizarre-but you know, people can be.... bizarre!) But I took note, that the vast majority of folks who were listing materials-just wanted to get rid of them. I saw lots of cool items, that I could make use of (but if I have any more hobbies, or projects, or "I'll use this in 6 months" items come home, my husband will KILL ME. ha ha) but there was a plethora of great things that were free, or ridiculously low priced, as another person, just didn't want to drive it to the charity or dump, and some places, (like where I live now) doesn't have one of those "larger trash days"- So I would encourage you to check out this section.
I don't have the skills to rip cedar board, build log boxes, or line with pitch- I suppose I could try, but I give kudos to those who have more handy person / construction skills than I, and just thought I'd throw these ideas your way, as I have been able to do small improvements on my home, with a little thinking and reaching out-for almost nothing. A local charity that "didn't know what to do with them" when they were donated- (awesome. It pays to your local thrift store, who you are, be nice, and leave a number, if they "get any building materials donated") perfect, 1930s era steel casement windows (huge!) that I am stripping and restoring and will eventually put into my house........ for $1 a piece. I am really into architectural salvage and antiques is my business- so I was.... blown away. Windows like that cost around 250-400 in their size and condition.
So maybe "if you don't want to go to a store", you could adjust that, and just... go to stores, like a thrift store, or charity, and introduce yourself.

I have even been given bizarre things (actually, ha ha, I think I was given a couple gutters honestly) because I had been talking about making a chicken coop, and I was trying to conceptualize a feeder DIY (so I screwed this gutter onto a board. and then used a smaller board to cover most of the gutter-instant feeder!
I wish you luck! people are mostly nice! just reach out.