Only the Queen can make you a lord: but you probably knew that already.
The confusion arises because in Scotland the owner of a large estate including typically a 'Big House' - not a castle - some tenant farms (having tenants to touch their caps to you is important) and the surrounding countryside, is traditionally known as 'laird' of that estate. A laird is not a lord: but the words have the same origin, and the scam merchants, of which there are many, have exploited this fact to the full.
So you can become a laird by buying property, yes. If you bought the whole estate of Ballantrae, including its Big House, grouse moors, and tenant farms you would be the Laird of Ballantrae, no question. You would be entitled to call yourself on your letterhead 'John Smith of Ballantrae', which would tip off everyone that you were a substantial landowner. But a laird is still a plain Mr, not Lord.
Also, if anybody else owned any part of Ballantrae, you could not call yourself Laird of it. But the scam merchants pretend that by buying a metre-square patch of land in eg. Glencoe you (and a thousand other people) gain the right to call yourself 'Laird of Glencoe' which is nonsensical. They hint further that as the words 'laird' and 'lord' have a common origin you can reasonably call yourself 'Lord' if you want, which is totally untrue.
Edited to add: a few days ago The Lord Lyon, the heraldic authority of Scotland, tired of having duped Americans apply for a cost of arms on the grounds that they are 'Scottish lairds', put out a press release spelling out the invalidity of the whole thing. Check out the link, and note that the scammers could only say feebly in their defence that Scottish law allows anyone to call themselves whatever they like...