Based on the examples of the ready bikes that you provided, what you want looks to be a gravel bike. If you're aiming for mid to top-brand components, you'll need to double your budget in my estimation.
Last year I built up a bike that I estimated to cost me £400, it ended up costing me around £800, even with low to mid end components, mainly because I had to buy tools, some of which were pricey, I had little experience, I made bad purchases, had to buy components twice, etc... But I ended up with the exact kind of bike I wanted, that I couldn't buy anywhere.
You may be able to avoid most of these problems because you have an experienced friend in the field who might lend you help and tools when you need them but if the bike you want doesn't feature any specific things on it that you can't find on any other bike, there's really no point in building it from scratch.
TL;DR: If you can find the kind of bike you want for cheaper, don't bother building, there's really no point if it's not a specific bike, unless of course you just want to have fun building it. Double your budget, or look for deals on ebay, much cheaper than industry shops like chain reaction cycles etc...
Kret
