Garage Roof Alteration, Planning Permission Needed? and advi

Hi, 1st post (so be gentle with me ) although have been lurking for a while.
We have had a problem with our garage roof with the felt coming off, it seems that we have a couple of options,
the roof is flat (slight incline) with felt covering, the felt looks like it was a real bodge job (we have been in the house 7yrs and was done ?when before this)
options appear to be getting the roof refelted with a small section of the decking replaced, had one quote £850 ish with 15yr guarantee
other option appears to be building up the roof to put more of an incline and tiling this (lean to fashion...not sure what this called sorry ) this sounds like it would be around the £2000 mark. Now I guess this would mean that we would not need to replace the felt every 10-15yrs, dont know if would need planning consent???
any thoughts on these options would be welcomed
thanks

Where is the garage in relation to the house ie is it at the front, back or side (in relation to the public footpath/road). Is it an attached garage or detached from the house? How high is it at present? How far from the boundary is it? Has the house got any other extensions? Are you in a national park or in a conservation area?

Hi Andrew
The garage is attached to the house at the side, set back a little fron the front of the house if you see what I mean.
I am guessing that the garage is approx 2-2.5m height but thats a guess to be honest
From the front boundary the garage would be approx 3 small-medium car lengths, from the next door neighbours boundary our and their garage practically touch so talking about inches
Other than the garage we have a conservatory extension which is width of the house
Not in national park/conservation area just bog standard street
thanks

You don't need planning permission to replace the roof covering.

If you alter the height of the roof, and this is outside of any permitted development allowance (google), then you will have to apply for planning permission and building regulation approval

Confirm what woody says, changing the roof from flat to pitched may come within permitted development rights. Was the garage built as an original part of the house? If not, do you know if planning permission was sought when it was added. Similarly with the conservatory? When was the house originally built?